While I am not sure how big the bubble is, I am sure that there is one, and that we are in one now.
Just looking at all of the tech fashion startups for men, and even accounting for the overall growth in menswear, I see a few issues:
1) Some of the ideas are really, really, dumb, and ignore things like "human nature" and "physics".
2) The pace at which there are new companies is outpacing the incremental increase in the demand for menswear
3) With more and more companies competing in the same sector, the bets investors are making are increasingly long, so it will become increasingly difficult to win.
As for "experts", I'm typically not that impressed, mostly because a lot of them don't take do enough groundwork, and/or rely on reports and standard metrics about a company rather than really understanding the meat. For example, imo, if you are not interested in clothing, you are much more likely to not see the glaring issues with a company that sells clothing.
While I agree there is a bubble, rapid activity in a sector isn't a bad thing. Economic theory hinges on the idea of competition; it would be much much worse for the sector if a few fashion houses dominated the market and colluded to influence prices (like the big 5 sort of did 30 years ago). All these start-ups restore (economic) sanity to pricing models; there is a lot more pressure on the established houses to either amp up design (allowing them to jack up prices or claim a differential of some sort over start ups) or to bring down costs (which is happening as designers pump out essentially two tiers of stuff). The market is becoming more efficient and more alligned to consumer tastes, whether thats quality or design or brand name bling bling.
On the other hand, competition fundamentally relies on human misery. Someone out there has to fail to make the market more efficient. Even dumb as hell start ups contribute some metaphysical value to the market as it more clearly delineates where the market is. Sucks for them, but its better for the rest of us. A bubble occurs when reality is uncoupled from pricing models. In my opinion, we are starting to see that in certain area's of Menswear (Alden Indies are selling for like, $200 more than they did years ago. Shell prices are going through the roof.), but I feel that the overall market for menswear has gotten better in terms of variety and quality.