In my experience (which doesnít include the most recent few editions), a new edition isnít about power creep so much as simply changing whatís powerful (and, often, a points decrease allowing people to buy, Er, bring more models).
Some stuff will get better, some worse. If s generally healthy to mix things up; lest we get stuck with an all-assault or all-shooting meta forever.
I guess, ideally, it would be perfectly balanced and everything would be equally viable forever. But in reality thatís clearly just wishful thinking.
Personally, I wonder what Primaris marines will do now that their whole range is out.
The most popular army is, generally, going to end up a bit more elite with a few less models o would think.
If wonder if that will make the currently ďeliteĒ eldar aspect warriors look very underwhelming, and how that will feel. Or if necron warriors will now look like a shambling undead horde in comparison. And I really wonder how todayís present horde armies will feel.
It almost feels to me like sisters are taking the place marines had. Thereís nothing wrong with that, and it gives them even more character, but I donít think theyíll ever become ďtheĒ main army, and I think it could be weird to have the new ďaverageĒ actually be really elite.
Not necessarily bad at all. But maybe weird.
Power creep could always end up making Primaris feel very average though, somehow. Although thatís a scary thought.