Given that you can't chose how a line is delivered with a silent protagonist - and no imagining it doesn't help, beacuse the way people react imply you spoke in a particular manner
No they don't. That's not how implication works.
You might assume that it does, but I get around that by not assuming it.
I don't know why you brought that up, and to be honest, you don't get to chose the full text of what your character says either. You get a list of things the devs wanted you to say.
A lost from which you get to choose, and if you control delivery as well, and there are no actions tied to the line, then you can have your character say that thing for a wide variety of reasons.
And if that's still not enough control, you can interpret the full text as an abstraction of the actual line (just as the keyword dialogue systems of old worked), thus allowing you to write the line directly.
Voiced protagonists add massively to the immersion of a game, and apart from the cost, I can't see any real drawbacks.
They make the character more difficult to control, and less mine as a result.
If you want a completely controllable player character, go play PnP. When it comes to designing video games, they should play to the strengths of that media, with things like voiced characters, rather than halfway-house systems like silent protagonists.
As I have argued many times before, I think the point of CRPGs is to recreate the tabletop RPG experience without the need for other players.
PnP is multiplayer. I play single-player games.