While everyone has their own personal preference on how they play I think its safe to say that most people don't like to play as a class where it feels like everything you can do can be done by other classes and probably better, as in 'why play vanilla Barbarian when Primalist exists?'.

And when it comes to maximizing AC the issue isn't only that DEX/Pyjama have a much higher ceiling but they can reach it with much less effort than armor+shield builds. Another reddit user who has an extensive knowledge on how to maximize your character's stats posted his 20 Tower Defense Specialist build and, by his own admission, that build still wasn't viable for Unfair. A class that is all about boosting defensive capabilites is made redundant by dipping 1 level in Monk and/or Nature Oracle.

Or if you're more familiar with D&D 5th edition, where for the longest time nobody wanted to play Ranger because both Fighter and Paladin with a bow were better at ranged combat and a Rogue's subclass was considered to do a better job at being a Ranger than the actual Ranger.