I'm genuinely curious about what people are doing wrong to NEED barrier to be competitive as an A-P.

If you insist on trying to take on groups of 3 and expect to kill at least 1 of them? Yeah, you probably need full A/B/S. Anything much short of that and seriously, you're doing something else really, really wrong -- and maybe you don't realize it because sometimes barrier lets you do it that wrong and get away with it.