-2 or -3 should be still acceptable. -5 is too steep for me. does larian follows monster CR? as i said if GWM is good for low level monster it wouldn't be useful for me. usually we wont have problems with low level monster anyway. in solasta even with advantage the miss chance is high too.
one noticeable enemy is warlords. if not mistaken having like 22 AC if not mistaken. i have like +10 to hit. to hit a warlord even with advantage you need to roll a 12 and above which is not so easy. such high AC i find using phantasmal killer much useful.
