Yes, I couldn't have said it better myself. Ulduar was, in my oppinion, the most successful raid tier Blizzard has implemented yet (both mechanically AND thematically).

Additionally, it's usually not bigger numbers that make a particular fight feel extra challenging; it's tougher execution requirements that really give a fight teeth. Achievements, more than anything, force raiders to approach executing the fight in a more difficult way (hard modes do too, but sometimes the major difference is higher health pools).

I also think the Ulduar way of doing hard modes made the two version feel less divided. Sure you were essentially doing different fights - but it didn't feel that way. It felt like the same instance, with the same bosses, and without any magical steroid pills given to each boss before hand. It was more organic.

All in all, I'd love to see a return to the Ulduar version of things. Heck, maybe Blizzard could introduce trash achievements as well - potentially spicing up trash pulls, while making everything feel more integrated as a whole.