You can't properly judge a girl's LTR potential just by looking at her. Or even determine her overall "sexiness" factor. You can just rate her appearance on the 1-10 scale, which doesn't really tell you anything beyond how good she looks in those pictures.
The best sex I've had was with a girl who was probably a 6. But she made up for it in other areas. Super smooth skin. Nice toned and tanned body with a round ass. Borderline obsessed with me. Super enthusiastic about sex and wanted it all the time. Loved giving head. Could cum from being fucked within minutes. Tight, smooth, clean pussy.
No one here would be impressed looking at pics of her, but of all the girls I've been with, if I had to choose only one pussy to hit for the rest of my life it would be her. Even though I've been with objectively hotter girls, I enjoyed the sex with this 6 much more, simply because all of those other factors combined to make my dick hard as hell. So while she may have only looked like a 6 in a picture, when she was naked in my bed telling me how bad she wants to be fucked, to my dick she looked like a solid 9.
So don't feel bad for our friend Felix, I think he knows what he's doing. Good chance he has similar situation going on with this girl.