Problem is that Fighting is supposed to be physical oriented, like how Psychic is special-oriented, general-wise at least.I will always remember Hitmonchan in the first three Generations. Access to the three Elemental Punches? Yay! Too bad it uses Hitmonchan's pitiful Special Attack.
Also, while some Fighting-type Pokémon have both good Attack and Sp. Attack stats (e.g., Blaziken, Infernape, Lucario, Mienshao, Cobalion and Virizion, Kommo-o), Keldeo is the only one to my knowledge who is specially focused.
But it did resulted too many “genericness” into multiple types in the long run due to poor variety over the eight generations, especially hurting Fighting due to too many mono-Fighting over time (fever pitch in Gen 8). Even Psychic have better variety by comparison.