Well, okay...there's a few things there I want to address.
First, I never saw Banaq as being remotely useless. Not in-character, not out of it. Spell resistance is a thing that has many counters, especially for a mythic character. And demonic foes of often have it, but not usually at high levels. The demon we fought that night in camp was specifically designed to be very challenging. It was way over our normal CR. Don't take that fight as an example of a typical encounter.
Case in point - the current clash. Tieflings got zilch SR.

Cultists, the same.
A flotilla of low level mages would have a lot more trouble with SR than you though. And they'd require a blocking unit to tank for them. And they'd get a handful of 'shots' before being done for the day. All in all, strategically, they'd probably be of limited value. Banaq himself, with his access to higher level spells, mythic goodness, and PC shine, could do more damage faster than a gaggle of magic missiles. In short, you ARE a mage battery. You don't need a crapton of apprentices.
Magic skews things. A hundred paladins is better than a single level 20 paladin. But a single high level mage is way better than a hundred low levels ones because of those save DCs, AoEs and caster level checks and other powerful spells. Magic scales differently, and favors experience quite a bit more.
Anyway, it's clearly your choice, and I respect that. I just hate to see you walk on what I believe are false premises. Banaq is important both mechanically and via RP. I also hate to think I had a hand in making you feel bad about your character and the game. I'd hoped for a kind of rivalry/frenemy type thing to develop between Thorn and Banaq...where they needle each other, but also kind of inspire each other to try harder, earning one another's grudging respect.
If I messed that up at the get-go, I take responsibility for it, but surely we can work something out.