Wizard is like the fighter - it's your job to inject the flavor. A blank canvas can be good for creativity...
My main issue with Wizard isn't its blank-canvas status (though I have issues with that too, for two reasons). My main issue is that it doesn't
do anything that's supposed to represent its core flavor concept, "magic through research." It would be like having a Fighter class where the mechanics
imply that you fight...but never actually
show you fighting. Yet Wizard gets a pass, mostly because spells are so stupidly powerful and diverse. That's a problem.
As for the genericism thing: (1) As noted, lots of people have "writer's block" type issues which can make totally blank canvases hard to work with. IMO this means for classes that are more innately blank slates, subclasses NEED to be offered that provide more flavor; it's fine for one or two options o preserve the blank slate, but when essentially all of them do, that's an issue. (2) Blank slates have a pattern of being either over- or under-powered pretty consistently. This applies most pointedly to Wizard and Fighter: the Fighter is the weakest or second-weakest of the "
more might than spells
" heavies (Barb, Ranger, Fighter, Paladin), and its need to be so totally flavor-free is a big factor. (Ranger is also weak, but mostly because vital class features got offloaded as so-called "optional" spells.) Wizard, meanwhile, can be stupidly strong because it's lack of flavor means it must go all out for "I cast lots of spells," and spells remain extremely potent tools in 5e. Again, not saying that
offering low-inherent-flavor options is bad. Just that there are oft-ignored design problems with such classes that need to be addressed to make them work well.