If you're happy to pay whatever it costs to host then there's no other disadvantage to this.
The only thing I can think of is if you somehow end up at odds with an admin of a big instance and they defederate your instance. Or perhaps in the future major instances decide to only federate with instances of a certain size, for some as of now unpredictable reason
Ah, right on.
Agreed on the value of the specificity, just in my experience you need to be ready to hold firm against bad-faith actors who try to rules-lawyer you.