The issue of "enthusiast phones" is not the same as for small phones. The problem that MKBHD is describing is that a company that starts as an enthusiast phone can not grow by getting the niche larger, so they need to start competing in the "average consumer" market. But a large, established company like Motorola and Samsung can for sure segment their product line to serve a particular demand.

I think the issue of small phones is that, while there people saying they would buy if it was available, no one is saying "I would buy one small phone at flagship prices, even if they don't have flagship features".

I suspect there's a large overlap between people who want a small phone and people who only upgrade their phone when there's a pressing need. I am in both groups.

The root cause is that the phone is not a primary device for me. It's what I use when bringing a PC is too much trouble.