Money buys quality and quantity
Quality × quantity = big race winners
Big race winners -> new owners plus more spending from existing owners -> money -> quality x quantity -> and so on, in ever increasing circles.
Quantities of quality makes a big difference. No “small but select team” anywhere for Willie.
Not really got an outstanding novice hurdler this year? Oh well, out of them all something will probably win one of the 3 G1s.
Arkle horse had bits fall off and a crap prep and next big 3 mile thing turn out to be not quite the star you hoped? Never mind, you can take your pick of jockeys to put on neat jumping second strings and win anyway.
Star hurdler out for the season and possibly, given his age, effectively for good bar maybe one lucky Morgiana or something? No problem, slot your good mare into the Champion Hurdle instead. Even if she stubs her toe the week before you can always re route Kopek.
Trying to hammer a Majborough shaped peg into a 2 mile Old Course G1 hole and realising it doesn’t fit? No problem, you’ve got the wee grey horse that hoovers up pounds sterling for fun.
Not really got a proper 3 mile hurdler? Never mind, that big engined failed chaser with its head on the floor will do a job and earn a few bob, and push your rival for the GB title from 3rd to 4th.
Star Gold Cup winner out? Not to worry, your stable jockey can now ride the new younger star.
And so on, and so forth, including the big money purchases that never even make it to the racecourse, or run in one maiden hurdle then fall apart and are forgotten about. The mill requires a lot of high quality grist. Not that Closutton is a mill, any more than anywhere else; Mullins has the unusual luxury of being able to tell owners that he is going to leave their expensive horse eating grass in a field all year if he wants. National Hunt racing itself is the mill.