Weapons do help a lot. This is, I feel, a critical thing to "get" as an AP. If you're mid rank, building up controls, you should not "lock into" one weapon set. A polearm, for instance, will dominate an assassin pretty handily and he's stuck trying to hope for a kot crunch while you're bashing away or nuking his strength. Crescent kick also works well but if that's what he's doing to you then you're in pretty good shape (generally speaking) so long as you don't over lag yourself.

Martial trance can change this but if the guy has sanc you can always just leave or maledict strength. There's no need to nuke dex, nuking strength will effectively do the same thing with the additional side effect of making kot/kans a lot harder to do. Try doing kot with a 5 str, I've had that happen and missed kot (like, outright misses), 4 times in a row (recently too).

If I'm a level 36 AP I'm building charges between different weapons because I'm trying to get fire control...and if I build enough momentum I'll consolidate them all into one weapon. And that one weapon will undoubtedly either be a polearm or whip just based on the mechanics of APs. You can shield cleave and faceslash, crippling strike, etc from the offhand.

If I had to define why APs who have access to barrier fail, I'd probably chalk it up to be built too defensively. You don't want to be defensive as an AP...that's what wands and healing preps are for. You want to be pure offense and control the lag so you can leave if you need to.