What's confusing about your critique is that it's very refutable. Eternum's MC does have flaws, the progression is already slow burn, and the game does already present a challenge. ...But probably not as much as you would've liked.
So what I get from this is that you admire the game's high quality but disagree with some fundamental design choices: You like it when the MC has more personality and prominent flaws. You also rather prefer monogamous relationships and want a really slow burn progression.
I get that and I would also like to see more high quality games that are like that. So, I'd really like to know which AVNs you'd rate higher than this one!