between no Tertiary Ability and no competitive ability,i'm totally against no competitive ability. Giving this cap a third "neutral" option wouldn't benefit the concept in the slightest since a neutral ability would reduce both the risk and the reward, so while it would be balanced, it would still be very counterproductive.
for other options actually flare boost have been the only one that have caught my eye. does it boost negates burn atk cut? if it does, i wonder how it would work if the best setup move this mon had was coil? a one turn suicidal mixed setup poke that could use stuff like blizzard or megahorn due the accuracy gain, and also coil could work in a curious way with weak armor. sorry for the polljumping though , but a coil flarebooster poke sounded interesting and a little risky :P
my options then would be NTA and Flare Boost.