The advantage dwarves have as casters under Tasha’s is really not significant compared to other racial features. Is it “better” for a wizard to have medium armor, or to be able to change their appearance at will? It depends on what you want to do with your Wizard. This is not the case when comparing ability score increases. Increasing Intelligence will always be better for a wizard than increasing any other ability. Racial traits come at the opportunity cost of other racial traits, which have similarly niche applications. Ability score increases come at the opportunity cost of increasing other abilities, and since every class has one ability that is objectively more important for them than any other (well, ok, fighters can choose which of two abilities they want to be more important), an increase to that ability instead of an increase to another ability makes a character an inherently better specimen of their class in a way that having one racial trait as opposed to another doesn’t.