[..] It worked in some circumstances. But plate armour kept changing, too. Why would it do that, if it worked so well, do you think?
Why are there various designs of plate bodkin arrows throughout the centuries, if they didn't work?
Why are people fighting with useless weapons, having their population train every Sunday from the age of 7, in the use of a pointless weapon, if they didn't work?
Why are the English famed for their useless weapons?
Makes no sense...
So why write it?
You're taking a typically extremist position, namely that the only things that can possibly exist are the two most extreme and opposing positions. Given that, it's not surprising that you sometimes write things that make no sense because reality is very rarely if ever like that.
Saying that armour worked is not saying that armour was absolutely invulnerable at all times in all circumstances, absolutely 100% total invulnerability that renders weapons completely useless. It simply isn't true that the only possible options are that arrows are completely useless against armour or that armour is completely useless against arrows.
There were various designs of bodkin arrowheads, but that doesn't mean they were designed for penetrating plate armour (or that they could do so). Mail is a much more obvious target for bodkin arrowhead design.
The fact that high quality full plate armour worked (and worked very well) would have been a very serious problem (though not completely nonsensical - see below) if everyone wore high quality full plate armour, but that was very far from being the case as you said yourself immediately afterwards:
For the nobility commanding, yeah plate was the order of the day... but the vast majority of their soldiers would have a cuirass over a gambeson, with maybe some maille between, and a sallet or similar helmet upon their noggin. The front line infantry did not fight in full plate, or anything close. Those are the main lot you need to kill, but if you happen to peg one of the nobs, it's OK... it's preferable to capture your enemy Nobs, though, as they're worth money in ransom.
The best case scenario for an army in that situation would be for their enemy to have plate armour that was completely invulnerable to arrows. That way the relatively few enemy soldiers rich enough to have full plate armour could be captured and ransomed more efficiently since they would be unharmed but vastly outnumbered after the less armoured soldiers were killed or fled or surrendered. Which was fairly close to what happened sometimes...because armour worked. Which is why people wore armour and wore the best armour they could get.
As for plate armour and arrows and nonsensicality...
Massed bow use makes sense even when against people wearing armour that gives extremely high protection against arrows. Even if only 1 hit in 100 did anything useful (to the side shooting the arrows), that's still useful if that army shoots enough arrows and medieval English armies shot a hell of a lot of arrows. Also relevant is the fact that quite a lot of the people who were wearing good quality full plate armour were mounted and their horses weren't armoured anywhere near as well if at all. Falling from a running horse that's been shot is likely to be a big problem for the rider. That's a lot of blunt force when they hit the ground. It's also a screaming, thrashing horse, which is both dangerous and bad for morale, and it's one less cavalry even if the rider was unharmed.
As for arrow vs breastplate, getting into that argument is as useful as gettiing into a katana argument and I'm not going to bother. There are plenty of videos for both extremes and some for a more reasoned point of view.