Throwing in a few hard encounters doesnt make for a challanging expansion. All in all wotlk is far easier than TBC and is generally catering for 10 year olds.
But really what really difficult encounters were there in TBC? Most people never did Karazhan before the first nerf, Maggy and Gruul were easy, especially when you had dodge-capped rogues for Gruul. SSC was the first real difficult one with two encounters that made you think and TK only really Kael was too hard. From there yeah TBC had the hard bosses but when you look at it what has WoTLK had.
OS3D, it was hard. Ulduar, it was hard. You can complain that some bosses were easy, but so was Loot Reaver etc, so in Ulduar you had AoC, Freya, Mimiron, FL, Yogg and Algalon which were all challenging with their HMs pre-nerfs. You had nifty achievements to try to get if you wanted to spice it up too.
ToC, like it or not the HM was hard for 2-3 of the bosses and you needed skill. ICC, LDW is unforgiving, DBS was difficult, PP was awfully awful and Sindragosa consumed our souls ten billion times, not to mention LK who melted faces very often.
Do I however think that the 30% was introduced too early, yes. It shouldn't have been introduced until 4.03. However you can't say WoTLK has catered to casuals too much, yes more people see raid content but thats not a bad thing. The encounters are much more interesting and 10m and 25m are both viable so not much more I can ask for.