It’s a tricky one. It really depends on how you define a big club. In terms of size and fan base, they are up there - they were getting crowds of 50,000 when they were in the Championship. That is pretty impressive.
I’m sure a lot of guys will say size doesn’t matter though
I’d probably place them in same category as the likes of Aston Villa. Not a big club at this moment in time, but a reputation as being big (ish) in the past.