- Meh is a form of expression and besides their expressions they have a persona with personality. In fact, being animated all the time is really bad for YouTuber. It's flat to be animated all the time and comes across as fake.
Meh tubers (That's not even what they're called. It's just a term I came up with) express themselves through a wider range of emphasis and tone. They ARE high energy, they're just not screaming at you. They're full of passion, they just really lean into other elements of vocal tone. It's actually very difficult to do but conveys an immense amount of information and connects very easily with the viewer.
Fingees Is my favorite example for this because he does it in such a way that you can actually hear where his emphasis is start and end very clearly, unlike other meh tubers who usually are more subtle.
And well, if I can, energy =/= personality. A guy who screams 24/7 is boring because there's no change, no modes, and above all no actual expression. It's just AHHHHHHHH and humans don't actually like AHHHHHHHH
And this ties into number 2 of your question a bit.
- This is actually a really serious concern. Do you struggle to tell apart the personalities of other people in your IRL? Or how about in your social groups? Most people actually don't have much variation in personality (and it's minor, more interest or preference based) But YouTubers have to have differences in their personalities and have uniqueness and memorability about them. Otherwise there's not much a reason to engage with them. It's part of being a youtuber, being someone people want to watch and engage with. There are a few exceptions (among the extremely old channels) but beyond that everyone is super notable persona wise.
If you can't tell a personas traits, I'd recommend trying in irl first. See what you find there where you have more context and physical cues to work with, then apply that to content creation. I'm sure YOU have a personality