Acid Purge hasn’t been nerfed at all, it has been buffed. As for the rest - Crit damage loss is not that big (how often does one Crit on bosses + if you already have Crit damage it’s even a smaller loss). A few % nerf at best, might be even 2% against a boss. I recommend the calculator for estimating the nerf. This is not Diablo 3 where %Crit damage is such a huge deal for every build in every scenario because Crit chance is high and independent of anything where it would be a 15% damage loss I guess.
In this build [1.1.9.0] I can't believe it's not FoI! Chaos "Acid Purge'' Warlock Acid Purge is not only in the title but also deals most damage if you calculate it. And it has more AoE than Doom Bolt which is another contender.
I haven’t done a lot of math but I believe for example you could make a very strong Pierce Chillspikes build (max casting speed and 2hander) where it can be the main damage source, at least for single target, so might not be build defining in Crucible but on bosses - sure.
Let’s not forget standard component skills can be cast up to 3 times per second and channeling ones can tick up to 6.66… times per second (ideal scenario, less in practice) if I’m not mistaken and this damage adds up.
I don’t mind you deleting this section if you so prefer - just stating my opinion as probably the main component / item skills enthusiast in the Grim Dawn community 