Sorry - there are just too many apologists to answer without getting shot from all directions. A guy before you excused this part of the plot by claiming that Euron had a large fleet on both ends of the continent, hence my hacking at his plot holes.
And to be honest, the more fan fiction you guys make up from thin air in your heads, the more plot holes you create as well:
If any ships saw them make the crossing (lets assume at night) they'd be torched by Drogon or flee out of the way so that they'd be too late to send warning.
Jaime and the rear of his army are out in the middle of nowhere so no ravens can get to them even if Dany was spotted. She knows he's coming back with the spoils from Highgarden.
Prime example - none of that exists, none of that was shown or hinted at. So in your head it might be perfectly excusable for Danny and Dorthraki to go and risk whatever she has left of her fleet on a whimsical chance that maybe, somehow, she won't be destroyed at Blackwater Bay this time, and maybe, somehow, Jamie was delayed and couldn't reach King's Landing
as fast as the gold caravans which were already safe by the time of attack and maybe, somehow nobody will react at King's Landing and wipe them out from behind.
Well it's semantics, since they made it to the ambush you can pretty much take it for granted they made it across the bay! They didn't know about Euron's fleet originally so didn't go with Dragons as cover. Even if they did they didn't know he's aligned with Cersei. Seeing as Dany is the only one who can control them would also mean she'd have to go with them. This time they went with the Dragon, even if Euron was close by, which he wasn't - he's coming back from the far side of the continent (by your argument he should have been around), they'd not be worried. The gold getting to KL worked against Dany, they clearly talked about gathering up grain and it taking longer so they only caught the rear of Jaime's army.
Who's going to wipe out a Dothraki horde, out in the open, that has a Dragon?! Besides nobody in Kings Landing will be any the wiser to what's going on.
Your raven excuse also works both ways - as far as viewers can tell Danny has not a faintest idea what Lannister plans are - any intel she might have had would be weeks old - from before Olenna died - the Lannisters attacked Highgarden. Then nothing. no one left to send her any ravens after the last of Tyrells is gone. Maybe Lannisters headed to Casterly Rock? Maybe they stayed in Highgarden? Maybe they beamed up with Eurons fleet back home in 12 parsecs. She does not know. It's not known or shown. So imagine this in the usual GoT pace - raven flies 760 miles, takes days for Danny to find out Olenna is in fact dead now (someone has to send that raven, you know, it's not on BBC News in the morning), then it takes days for Danny to make a decision (as we witnessed), takes a good weekend and a half for her army to cross the channel and get to the Blackwater Run (armies on horses travel 40-50 miles a day) . So in most viable scenarios when her Dorthrakis emerged from behind that hill at full speed, pony tails flying, hooves screaming in corners - they should be expecting nothing but a few sheep chewing grass. But this season all logic is skipped for a good scene. And a great scene it was, but it would take what - 2, 3 minutes, two scenes max to build it up to exactly the same payoff without any plot holes?
They knew Casterly rock was emptied, they know they rely on Highgarden to feed her armies - they heard it had fallen and presumably sacked. Where else would they be taking the food and gold? And it's not that hard to believe it'll take Jaime's army (which is on foot) a long time to cross the country with those caravans.
What I'm saying is -
unlike in previous seasons - in s07 there is no supporting plot, no prep, no back story to most things - as far as we can tell, from what we witnessed as viewers Danny should not have the faintest idea where her enemies are. And TBH - one of the best things about previous seasons of GoT was that intel was realistically slow and dreadfully unreliable. Entire battles and thrones were lost and won on bad intel and allies turning up without the other side knowing they were even in the same kingdom, let alone coming with rescue. Those that mastered intel - Varys, Lil'finger, they were the top players of the court. But in season 7 suddenly everyone has motherloving fleet of military satellites. Danny has not been to Crownlands in her life, but can do raids on moving targets 100 of miles inland, past the biggest stronghold on the continent, with GPS guided drone strike precision (snaps fingers) like that.
What's worse - all of that is served to us as "before/after lunch" - without a slightest attempt to give us impression of distance and time. And I know you are going to claim it happened before, but no - s07 creates these editing errors like it never happened before. I don't recall ever before being confused by time frame and distance in GoT, if anything, we knew it was going to be a long journey, it would take characters entire season to move across two towns sometimes. But suddenly we have these lapses - Danny asks Jon for advice while walking up to the castle from the beach, we have a scene with Arya and Brienne, then we see Jon walking back from the castle presumably after escorting queen to the door, but no - it's now a week later (don't you know?). The sun is the same, the beach is the same, everyone is dressed the same, darn how do you not know it's next week thursday - isn't it obvious? Now look, I'm not asking for "7 days later" appearing in white letters on the screen, but there are thousands of ways they used to give us impression of time - how about Onion Knight starting conversation with Jon on the steps just a few lines earlier "Haven't seen you entire week Jon" "I was busy in the mine, still trying to figure out how to make weapons out of Dragon glass", "You know, there is a good weapon smith in town, I saw him in his boat rowing by just this morning, maybe we can visit him in the next episode". There (whacks the table) - time passing by arranged (and those that pay attention know who I was talking about as well - would be typical GoT wink-wink scene).
Even if the 'Jon advice' and then Jon, 'she's gone' to Theon are the same day it doesn't matter. The next scene with the Lannister can be presumed to be three days later or however long it takes to get to the ambush. Why? Because they turn up to attack Jaime. Simples. We did NOT need filler in between Jon saying she's gone and the attack. That'd kill the pace and flow of the episode.
They used to do it, they don't do it anymore. Because they are lazy. Because they can't be bothered. For all the money they took from HBO and all the hours of this magnificent story they stole from us, they cannot be bothered to end it with coherent, water tight plot paying off years of fandom, plot worth the TV benchmark logo on the front. I'd rather they stopped focusing on some irrelevant starlet cameos and kept the old visual pace and delivery. When they want to show me homage to earlier season, when Arya arrives in Winterfell and gets interrogated by the guards I would prefer if they remembered she had a horse and luggage 5 seconds before in previous scene. GoT never done such continuity errors before, so I can only presume that large chunk of her return scene is missing. I wouldn't mind if instead of Sheeran chalkboard scratching some camp fire song, they showed me that Arya gave her horse and belongings to the first beggar on the bridge - as long as I don't have to patch it up with some made up fan story on overclockers forum. The homage scene would still be just as good but those of us that noticed Arya lost her horse and bags would know we are not watching footage that's been dissected five times to fit in as little scenes in as little episodes as possible. I feel we deserve it. Especially with 14 fatherforking minutes to spare...
Blimey, that's some epic level 10 bitterness. You were acting like they'd spat in your cereal the moment you heard there was to be a shorter season. I think you're just projecting your bitterness at that decision into the episodes which are, btw brilliant. Their decision, btw is quite justified given how many set pieces they're showing and the budget, time it takes to put these in. We're into the end game, a lot of things are happening so the pace has picked up. 'Can't be bothered' and 'lazy' is just... ridiculous.
I'm enjoying it. But I would enjoy it even more if they stopped rushing stupid as if it were last season of Dynasty.