And ruling NOT to add any house rule is perfectly legit.
Rulings aren't 'house rules,' they're a necessary DM function, especially in 5e, where essentially every action resolution technically includes a ruling from the DM.
What I quoted is the RAW and that is the starting point for everyone. Just because you don't like it and don't want to play without a house rule on top of it, doesn't mean everyone should do the same.
The thing about a starting point is you move on from it. The Rules of 5e are Written, as much as possible, in natural language, so they are naturally ambiguous. When the rules aren't perfectly clear & explicit, you make a ruling, deciding which plausible interpretation to use in that instance. When the rules don't cover something, you make a ruling, deciding how to resolve the action that lies outside their scope, or your game halts.
Your ruling is that a spell with verbal components can be cast under water, even by a caster who'll drown there, and will work normally. You dismiss portions of the rules as flavor text, which is exercising judgement - as a DM, in your campaign, you have every right to do that, so it's not a criticism or anything. But, it's no more or less a 'house rule' than any other DM's ruling.
If you formalize it and stick to it, it could become a house rule. Even then, as more situations come up, you'll probably need to make rulings about your own house rule, anyway, to keep your game moving.