I suppose opinions are just that. I for one liked both SoI and the Ultramarine series (DSBS in particular).

IWs shouldn't be like this, their protayal has nothing to do with what GW had established before (Chaos-following IW make no sense, sorry, a IW would never ever bother trying to become a DP...)

That would actually be newer lore. Storm of Iron predates the Horus Heresy series by... I want to say a decade? And it's been ten thousand years in the eye of terror.

They aren't word bearers. They make practical use of chaos. I would say it is entirely within their character. And Iron Warriors would absolutely try to become Demon Princes - their primarch being the prime example (again, according to old lore that hasn't been changed yet. Which is still canon).

In fact, I hate Angel Exterminatus because these totally non-IW lads for some reason were big fish during the Heresy. It's a pity that the only book to get Pert right is so wrong overal...

It's been a while since I read it, but what made the characters non IW?

I will be honest with you. You seem to have a perspective on the Iron Warriors that conflict heavily with established canon, both HH and older 40k lore. Or in other words:

You are wrong. Or referencing fanon.