Chaosmancer
Legend
Yeah. For instance, Gloom Stalkers are skilled at fighting Aberrations and the creatures of the underdark, but they're not bad at others. A Monster Slayer has features for fighting undead, werewolves, and the creatures of the night, but they're useful against everything. Giant Slayer, Dragon Slayer, Beast Master... It's a thematic thing to hang their hat on.
It would be thematic, but it would bring all the problems that favored enemy carries only dialed up to 11.
Again, I am looking at the paladin. The paladin has great tools for fighting undead and fiends, they are phenomenal at it.... they are also really really really good at fighting dragons, aberrations, humanoids, golems, elementals... you never feel like "if we don't fight undead or fiends, my abilities are useless" It is more like when you do get to fight them you feel like "awesome, my abilities just dialed up to 11 instead of 10"