The only caster I don’t like in SFR is Goreshade3, because his best spell does nothing, and SFR doesn’t have great models for his Feat. I can even entertain Terminus in SFR because of how crazy good Bloodgorgers & Gerlak are at getting him souls on Feat turn.
I actually really liked Asphyxious2 in Slaughter Fleet. IMO, I actually think SFR makes way better use of Asphyxious2’s Feat than Dark Host does. Before I picked up Skarre3 I was playing:
What you choose to Feat back depends on your opponent’s army. Your opponent playing dude spam. Feat back Bloodgorgers and Pac-man through the dudes. Opponent playing high value constructs, Feat back Iron Mongers. Opponent playing high value living models, Feat back Smog Belchers, turns out they just hit at casual base pow 13.
Asphyxious2 Dark Host cracks armor very well, but it doesn’t have a whole lot of answers for dude Swarms. Asphyxious2 SFR is slightly worse into armor spam, but is way more versatile and can play games into a lot more matchups.