Thanks for the comment, James, interesting stuff. I've heard that before, and used to think that for the same reasons, but it seems that is not the case, or at least historians say otherwise, you may find this link of interest:
This link also provides a decent roundup:
https://stageswest.com/blog/myths-about-western-wear/
A quote from the above:
"Men almost always commonly wore hats on the American Frontier, but derby hats (an alternate name for bowler hats) at that time were the functional choice as they stayed put when it was windy and could be worn for all sorts of occasions. At that time, too, frontiersmen wore hats that were related to and assisted them in whatever employment they had. Commonly made out of beaver fur-felt and natural in color, derby hats and flat wool caps, Mexican sombreros or old Civil War hats were the norms."
Hope this helps, and I think the thing is a cowboy hat is classed as a wide brimmed high crowned, and so it’s got a distinct design. It’s my understanding that a lot of the pictures don’t actually show cowboy hats per se, they just show variations of hats of the time, like sombreros, or Spanish influenced style hats, or adaptations of derby hats/ bowler hats et cetera.
So, you think you're looking at a picture of a "cowboy hat" when actually you're seeing an adaptation of a sombrero or other hats from the time.
The Stetson itself, which defined the cowboy hat, was an adaptation of these styles of hats, hence, similarities to them. I think as well, what gave the bowler hat a.k.a. the Derby hat the advantage, was that it was created in 1849, and immediately became popular, and as the archetypical Wild West era began in 1865, it was simply just good timing. I believe Stetson didn’t invent his first hat until 1865.
But anyway, thanks for the comment, interesting stuff!
