Go and have a look at what Guardiola, Messi, Stones and Hart tell you about playing there or ex players who will admit when they went there they didnt think much of the size of the club but when they left they 'got it'.
They have probably just as big a fanbase as Everton, play at a higher European Level and whatever you think of Scotland, win cups. Also try getting an away ticket for a Celtic match, its fucking solid. Everton is way easier.
Having a decent atmosphere doesn't make a club big. Celtic are big in Scotland and Ireland other than that they're not a big club and haven't been for a long time, the exact same goes for Rangers. As for winning cups, it's pretty hard to finish second in a one horse race and even with Rangers doing well, the odds are still pretty good in a two horse race.
Anyway, this is an Everton forum so lets talk about Everton and their left backs rather than make it into a "Celtic's better than Everton" thread.