I’d definitely class Mav, ellsworth, ibis, turner etc as boutique. I’d say boutique is non mainstream, pricey, rare.
So, is cost a primary signifier in what constitutes ’boutique’, then? Cos stuff like On-One, Ragley, Merlin/Rock Lobster, Cotic etc aren’t particularly pricey, yet not readily available in Evans, Halfords etc. Indeed some are only available via mail-order and not through any shops, and only in relatively small numbers. Plus, stuff like that is designed at least by a ‘bloke in a shed’ type set-up.
Seems that ’boutique’ translates more to ‘expensive’ than any other consideration, for some folk. Regardless of how good the bikes actually are. Spesh R+D, testing and pro support is way way in excess of someone like Ellsworth for eg, so surely Spesh could well produce the ‘better’ product?