Depends, I believe a healthy relationship would just need average looks, or even below average looks in certain cases.
But thats in the premise of a ‘healthy’ one which, with how I view it, is just two people trying to make things work over minor affection towards each other, not to the point of genuine love as in near devotion(but not complete devotion) together but enough to feel better around eachother.
Just because you are comfortable, does that really constitute as love?
Not really, most relationships dissolve due to this; and in modern society physical attraction is just too important to dismiss (for lurkers, even if you want to dismiss the notion of someone needing to be attractive in beauty standards, it’s pretty obvious one should hold some physical attraction to their partner in their own opinion, right?).
Even people well-off, rich etc would have partners that don’t feel much towards them outside of faint affection and comfort; which is more contributed to the lifestyle they provide rather than the individual themselves.
It’s weird to say it like this but it seems closer to a close friend that you share with and would sometimes feel more daring towards rather than a connection that both sides are heavily invested in.
Relationships are naturally more devoted and intimate once there’s physical attraction involved as well, it’s just a natural reaction.
HTN is a pretty clean bar for this, as in a general sense they would be seen as just attractive by the general population, meaning most people would see them desirable enough for that intimate connection, maybe they won’t hit the mark at first but they eventually do.
There are of course examples of ‘genuine love’ relationships existing well below this bar, but let’s not pretend examples that only constitute the minority of such relationships somehow means majority of people below that bar will find it.
And below MTN? Good luck

even finding a long-lasting transactional relationship is utterly outlier in that regards, forget genuine love.
Though, in the end my definition for genuine love is artificial at best; I struggle to comprehend something I never experienced, not even from my (lack of) parents.