I'm not sure why some fans talk about supporting a big club as some sort of badge of honour. The mackems are the prime example. They constantly like to remind people just how big they are with their attendance this and attendance that drivel.
Sunderland are the biggest club in the EFL if big is defined solely by attendances. But that also makes them the biggest failures as they've achieved nothing for over half a century. If big is defined as success, then Bury are bigger than Boro, as they've won 2 FA Cups to our none. And Preston are bigger than half the current Premier League as they've won the League and done the double. So success alone does not always equal big imo.
Personally speaking, I'm proud of Boro precisely because we're not a big club and never will be, but we've held our own and spent 99% of our entire history in the top two divisions. I've seen us beat the Arsenal 'invincibles' - twice in two weeks - to reach a major final and go on to win it, then compete in Europe and reach a final that only a select few of British clubs have ever managed.
Give me 'little Boro' and its achievements every time over some forever sleeping giant that hasn't achieved anything since the days of black and white TV.