I think that you can have both, but you can't always have both. Because it doesn't always make sense to.
Its almost all about projection. You can come across as a "quiet" speaker and still manage to be heard when you're projecting and enunciating properly. Projecting isn't about being loud, its about being heard.
I have a tendency to mumble a lot when I'm not thinking about it. Thinking about projecting my voice brings things across better, and its not really all about being louder.
On the other hand, I'm not sure what hyper-realism would contribute to something like Star Trek. The show confidently embraces the fact that it's basically a bunch of fairy tales for nerds. That's what allows it to be as great as it is.
Not everything needs to be The Wire (even though that was great too, if you enabled subtitles).
But, if I hadn't seen maybe two episodes, I might have the same impression.
How often do you see Captain (!) Picard out of uniform? The character of Picard-as-officer is constantly on stage, he's the master and commander of an entire starship!
Second most often, we see him on the Holodeck, where he's playing a captain playing an actor playing a role! Of course he chews the scenery there.
But when we see Jean-Luc, the civilian, something changes. All the Royal Shakespeare is invisible, he's an old man who carries a great burden, and has put it down for just a moment.
Patrick Steward is very, very good at what he does.
omg that's embarrassing, but I guess it's true
You can have both though. A great example is Patrick Stewart as Captain Jean-Luc Picard in Star Trek: The Next Generation. He’s never mumbled a line in his life and you can understand everything he says during quiet dialog. You can be true to life, quiet AND understandable.