I though I already clarified that both situations are 1v1 but I guess not. Obviously if you are teamfighting you want to use that A to get BP stacks and barrier. But if you’re full built and use that in a 1v1 scenario where both of you are standstill you’re losing DPS from the animation of the A. The A has the tiny amount of time where you can’t do anything (as can be seen when you try to consecutively dash). Time is crucial for an AA hero who just wants to finish things off fast yet get the most out of it.
Regardless you use his abilities to get the most out of his AA anyways, they aren’t meant for damage but instead CC/catching up. BF on the other hand gets the best of both worlds. His A can be used to chunk hard, his B used to do damage and apply a barrier on you (no matter how small) and his Ult is basically a reflex block, dash, and triggers basic attack effects. I wanna say that Kensei has terrible WP ratio’s on his abilities rn but I don’t think I can recall that properly or not.