“Boutique/premium” bicycles are mostly just another Keeping up with the Joneses/wealth display thing now aren’t they
But define boutique? Boardman, On One ,Vitus? Or Townsend, Barracuda BSO’s??
Some folk are happy with a £100 bike, some with a £400 entry level Trek.
I think MTBers buy quality , quality costs. You can ride a £100 bike around any trail centre. Probably never again, but you could. We buy what we can afford.