To be fair,IMO, their natural realistic level given their support base ,ground, etc, without big outside investment is as a championship/L1 yo-yo club. With a good manager and some stability they ought to be able to live as an established championship club.
I'd put them at the same sort of level as say Preston North End or Burnley -- a club wth a massive history, and lots of tradition, but never in the foreseeable future going to be an established premier league team. They might get odd moments in the sun, as have Burnley recently, but they won't last, unless they ever get a serious and genuine fan-owner like Blackburn did.