The funny thing is that, Only War is at a lower power level than even DH.
Starting PCs are roughly at DH level, except with better equipment. But everything is more expensive.
What you said is as meaningless as a technically true statement can get.
Every game past DH prices advancements higher than DH. Every game with advancement charts past DH is more restrictive in what Talents it allows at what ranks than DH is. Every game except of OW is just getting started at the experience level where DH is either midway to or just entering the extremely broken endgame of Ascension. Deathwatch Marines are supposed to be the most powerful characters you can play, but Ascension chars make them look like retards.
Therefore, comparing any progression to that of Dark Heresy is pointless. And really, comparing the exp progressions of any two 40k games will yield strange, counter-intuitive results - generally, the more powerful the characters start, the slower they progress and thus the weaker they get compared to those starting from a lower tier as time goes by. Those "experience levels" for comparing characters from different games are rough guidelines at best, completely useless at worst.
There is no truth in flesh, only betrayal.
There is no strenght in flesh, only weakness.
There is no constancy in flesh, only decay.
There is no certainty in flesh but death.