Rangers ARE a big club. And an important one, especially in Scotland where the high level pro game is tenuous at best. But they have proven over and over and over again through multiple ownership and management groups to be bad stewards of the game and selfish actors in Scottish football. It's always, 100%, all about Rangers to them. Always has been. Celtic aren't perfect ... far from it ... but when the time comes to suck it up for the greater good, they're usually on board with the big plan.
I mean, it's hard to say isn't it? They do draw 50K for every freaking home match (even against the likes of Ross County) and travel as well as any club in the UK. On the flip side, they don't have the international brand impact of clubs who have spent the last decade in the Champions League spotlight, and don't even really match up locally with Celtic in that regard either. But that stuff is hard to quantify. I'd say in terms of impact in the UK alone, they're on par with the likes of Villa, West Ham, Everton and Newcastle. A big club, but with mostly a regional footprint.