Has Warmogs become the new GA, I see everyone get it ADC, APC, hell I've even seen some supports get it as a last item, is it just really strong or has GA just become really weak?

Resistances were hit pretty hard for this season but health remained largely unchanged, to the point were health is 2-3 times as effective as resistances for the price - not to mention nondiscriminatory to physical, magical, and even true damage as well as un-mitigated by armor and magic penetrations, and armor and magic penetration got a significant boost into this season.

So for your question I'd say it's a variant of Guardian Angel is really weak, (I'd just put it at slightly weaker) along with all other defensive items that offer resistances in comparison to just flat health.

warmog's 1k hp is about the same as guardian angel's revive if u include all the armor/MR probably a bit weaker but the fact that u don't need to wait 5 minutes to recharge makes it just as if not better.