i tried chieftan ba in legion and it was fine at clearing packs with prolif but i wouldnt say it was any better than most other skills.
it was very bad at trying to clear frozen legion monolith enemies just because its slow, even with gmp and chain
bosses and even high life rares were really bad to fight because after spending all my vaal ba charges it would just be spamming normal burning arrow and thats just not fun
although i do have to say it was actually fun to play it, and using vaal ba on bosses (if theres enough damage to kill them) looks and sounds cool.
my damage was just not enough for late endgame like red tier bosses, legion bosses, shaper guardians etc and im not sure how much optimization it takes to 1 shot things (and by 1 shot i mean all vaal ba charges with a second or two in between to let burning damage tick).
maybe my gear just sucked but even with a little more damage the playstyle just seems like too much effort
dying sun seemed good to me. even with gmp its very easy to miss burning arrow and more proj helped