Any costume that's a uniform other characters are seen with, like a school uniform, should definitely be a <x> uniform gentag rather than a Fujimaru chartag.
I'm torn on one or two of the Fuji uniforms chartags (like True Ether) because they /are/ uniforms but we've never seen anyone else wear them - but in general a lot of them should be gentags instead.
Stuff like Mage's association, Combat Uniform, Polar Uniform, Decisive Battle Uniform are actual uniforms which characters other than them can maybe seen wearing, like post #5400079. (I'm not sure on all of them?)
Then you have stuff like Anniversary Blonde as a chartag too when it's a literal cosplay of another character...
At the very least something like the Souya high school uniform should definitely be a gentag, it's literally the school uniform from Tsukihime and has essentially nothing to do with the Fujimarus beyond being a borrowed outfit.