Were there other companies that attempted what Stitchfix is doing? Trunkclub and Stitchfix were early movers in this space as far as I am aware and others have copied them.

Didn't get your point regarding whole sellers. As far as I understand this industry, the retailers generally source directly from brands and so does Stitchfix.

"their market position is dependent on their ability to match clothes for people"

That's their core competency though. That's what makes them successful.