I don't understand how silence "hard-counters"... I mean it blocks most casting for a round but it's only a 20 foot sphere, that can easily be moved out of. Yes it gives like one turn of disabling a caster, but honestly, lots of spells give that already.

Dilligent casters in a magic heavy setting probably know the dangers of silence and have prepared ways to work around it.

I just don't understand how it's possible, like you say, "hard-counter every boss". In specific situations, sure. But "every"? That would seem to me like just not a very smart/tactical DM you play with.