Touhou actually has an extensive collection of doujins and manga attributed to it, so the whole "it doesn't belong here" argument doesn't fly. Even more so since it's still relevant to the tastes and interests of a great majority of /a/'s base.
Also, no, it wasn't a problem. Generally, they kept their shit in one thread. Hijacks were the work of a small handful of posters (Russia's bot and maybe two other guys)
/a/ will always, ALWAYS have content you find disagreeable. You just have to learn to live with it rather than demonizing its proponents >>10868259
Not really, /a/ has always complained. The problem is that the board was split when it didn't need to be.