Yeah, basically the way I would put it is that with ONLY PHB1 you have a bit of an issue with most classes having limited options. In that sense PHB1 classes are a little bit underpowered, but it isn't because they're underpowered classes, just that this and that added option has come along since then, which they can fully take advantage of.
The evolution of the power curve in 4e IMHO has been kind of odd. PCs started out at low levels being somewhat low in damage output, but monsters were as well. Combat felt like chipping away at the enemy a lot of the time. There were also a few totally OP things though, like Rain of Blows. AV1 jumped PCs up quite a lot with the ability to get better superior weapons, many really advantageous bread-n-butter items like Iron Armbands of Power, etc. PHB2 tossed in quite a few more really good feats. This pretty well put heroic tier PCs where they should have been, but came close to breaking epic entirely.
Then WotC came in over time with a lot of nerfs on key things that people abused, and finally MM3 monsters showed up. Now combat is fast and furious and as long as you take your lessons well on how to design monsters and encounters epic and high paragon are working more as intended.
Basically if you're making sure to boost damage on MM1/2 monsters and adjust their defenses and HP down where recommended and using at least AV1 and PHB2 for extra options there really isn't power creep, just refinement. In a strict numerical sense, heroic tier and paragon PCs will mostly do more damage now and hit more often, yes, but they will also get beat up more and be much less able to just end key encounters right off the bat. 4e keeps getting better, which is a good sign for a game that has evolved this much.
