Sure there's several factors that play into bringing home the ultimate prize.
Being able to put a quality team around your QB is definitely one of them and you have to have money free to do that. When you tie up ~20% of your cap space into one player , its damn hard to fill the other 54 roster spots with enough quality.
The magic number so far has been below 13.2% which , again was the very first year of the salary cap era - 1994.
I'd say that much history is pretty telling when we've had some really great QB's in that time period earn greater amounts and every one of them failed - Brady , Brees , Favre ,Warner , Aikman , Rodgers , Peyton , Eli , Roethlisberger , Wilson.
Every one of those guys won superbowls (19 among them).... Not a single one did it earning anything close to 13%.
They had to have money to spend on quality players around them.
Nope , its not the only thing but history shows its a starting point - That's why in this era of football the best chance most teams have to win it all is in their star QB's rookie deals , once they are playing in their second contracts , they tie up such large percentages of the cap that its just about impossible to put enough players around them.
The Texans mistake wasn't extending Watson , it was failing to take the impact of Covid on the cap into consideration. They paid him like the salary cap had continued its $10m per year gains.
If he won't reduce those cap hits in 22 & 23 they'll have a hard time putting much talent around him and that's a fact.