You may be hitting the root of things.
It kinda feels like the specification of "powers" is a debate gimmick.
In actual play you don't parse out things like "my class" vs "my class' powers". You just play.
People complain a lot about the endless +3 to a skill feats in 3X. I think that would be the ultimate definition of "samey". Yet I've never heard anyone claim that feats are samey. (As opposed to "New splatbook XYZ is full of feats with nothing new in the bunch". So you don't like the product.) But when actually playing there are plenty of diverse feats to choose from and 3X as a system, doesn't have nearly the equivalent "saminess" reputation as 4E. (YMMV, but as a collective perception, this is true).
Joe plays 4E. To Joe "everything" feels samey. Joe burns out on 4E quickly. Somebody tells Joe that "powers" are not samey. Joe, having not played 4E in month shrugs, it all felt samey to me.
Add to that the fact that there are reasonable arguments that 4E powers are at least a bit more samey (the math, the presentation, etc) and the point becomes so fine that it is meaningless to the real perception of "fun at the table".
Yeah, but in the same vain we had a thread here splitting up the spells to make 5e classes less samey.
Or how in late 3.5, every character was squeezed into 7-10 archetypes because so make feats and spells where straight bad or vastly underpowered.
Sameyness in classes, spells, powers, build, etc all have different priorities based on the makeup of the table members. Which one was important depending on your group.