I was thinking this the other day. From an early age I shaved daily for many years, and only had one brush probably a boar or cheap Badger. Like many I graduated to Carts, and when I started to get skin problems reverted to a Gillette DE.
Somehow, looking for new Razor I came across Shaving Forums and Rabbit holes appeared.
The biggest Rabbit hole being Razors, and though I have a few brushes I managed to limit it to about 15, and no high end ones.
Not sure that an expensive brush improves a Shave, exfoliating !! Is it a myth ?. I can use the humble 404 mixed and provided I get it whetted it coaxes a beautiful working lather from any soap.
So we probably could all manage with one brush if push comes to shove. But Gents keep buying, because I enjoy looking at all the beautiful ones shown in SOTD.
PS Used 404 today with MWF in Chalky Kent and had lovely Shave.