I don't disagree with what you're saying in a general sense. Creative people output will be better and higher quality than an algorithm...But I don't think that's the case for this business model.

Although I believe there is creative merit in composing an clothing outfit I don't believe that merit is even remotely close to things such as designing the actual clothes or creating the drawings and art that goes into the clothes or designing the stores in which these clothes are sold...

So I stand by my original statement. I do believe an algorithmic stylist for the avergage person can be vastly superior than a human stylist, because the inputs that the former takes are not that different than the inputs of the latter. Furthermore, the reasoning is essentially the same:

People want good fitted clothes, that are in fashion and that go in accordance to what they like. I don't think there's a lot of room for creativity here. I'm sorry that it sounds like a machine-learning nihilist take, but in practice I don't believe there's a good match between what people want from something like Stitch Fix and what a human stylist can do for them.

I dooubt that someone who relates to clothing in an artistic way would ever use something like Stitch Fix, so my assumption is that for the average Stitch Fix user, an algorithmic stylist could give them the same desired output at a better cost.