Erm, to some extant, there will always be a "toughest unit/codex", I'm not sure we can waste time worrying about that. Yes, banning 2+ rerollable will make something else the nastiest unit out there, but that doesn't mean we shouldn't do it. It's an obvious unintended loophole in the rules.
I think it's clear that the only reason that Escalation exists is that GW was sad that too few people bought their apocalypse book, and they made all these big fancy models for it, so they're trying to force the issue and somehow say that you "must" allow apocalypse units in 40k. I see no reason to support them in that.
Stronghold, on the other hand, sounds like it has a bunch of "optional" rules that are really clarifications for fortifications rules (which have never been very clear) which should have been in the main rulebook from the beginning. Since they screwed up the first time, these should be in a FAQ/errata. But GW has apparently decided they don't need to do free FAQs anymore, they can just charge you to fix their bad rules.
It seems likely we would probably want to use those "optional" rules. I don't think that means we have to allow all these alternate fortifications, and certainly none with D weapons.
Also, it sounds like Stronghold has no Xenos buildings, none at all. Screw you, GW!