>>96747430
>Right, I get that, but explicitly why do you want them to have this unparalleled flexibility? Not a criticism, mind you, just something to think about.
Because shields are cool.

Swords have lots of masteries associated with them (sap, vex, graze) because each is a different weapon. 5e doesn't really have more than 1 kind of shield, baring some magic ones, so the weapon masteries let you have a sense you're using different kinds of shields. Push/topple could feel like a heavy tower shield, nick and vex are affiliated with fast and light weapons so you might feel like you're fighting with a buckler. Cleave or graze can give you the impression that your shield is bladed or maybe has a spike etc.
>There's this implicit "intent" you have behind the feat, that it could or would only be used by fighters.
It's a feat and fighters have extra feats, so that's understandable. But any barb, paladin, or ranger who wants extra AC for survivability and a bonus action attack has it available. Paladin and ranger have access to two weapon fighting, and barbs have rage damage so they don't fall off too bad.
The sword and board fantasy is so iconic, so I'm just let down that there isn't much to it, and locking it behind a single fighter subclass didn't appeal to me.