Exactly. Outside of the Big Six there are no 'established' clubs, just clubs that haven't been relegated for a while. (Or not at all in our case - PL era only of course).
It's a bit like being an alcoholic (bear with me). Honest alcoholics always admit that, not matter how many years they've been 'dry' for, they are still alcoholics who could easily sink back into their old ways if they take a drink. They know they will never be truly 'not-alcoholics'. And all clubs outside the Big Six are only one bad transfer window and one sub-standard season away from the drop.
It's not just about money. Good organisation and good scouting are essential. You have to be a better club than the three that come up, and those guys only get a few weeks to put a Premier League squad together, whereas for the likes of us we have a whole team of players out on loan.
A well run club from top to bottom, with great long term owners (not necessarily financial doping to success), genuinely healthy income streams, a good academy and scouting.