So, what we know by now, is that his (and his sister's) parents love, has all this whole time been totally conditional, on the expectation that they have enough magic power, to live up to their "family's name"...?
(And to be precise, not just the "love" has been conditional, but even fact if he's been treated as a normal human child..)
Because of that fact, since MC had "unwanted" result from one test, he has been abused, beaten, shunned, disinherited, by both of his parents (though only daddy used violence), we could say for a certainty, that the parents have shown their true colors/faces, and the type of people they are down deep...
Oh and we gotta remember, they would treat his sister w/ the exact same way, if she had the same results from her test...
My problem isn't really all that, even though the father's brother/MC's uncle, is a very successful person in life, even if he had the same starting point as MC...
My problem is, W H Y is MC so interested on pleasing his shitty parents/family, who happen to be total garbage as people..?
If this protagonist had self-respect, he would either ask his uncle to adopt him (since he already has been disinherited by his parents), OR just back his things, and leave (now, or when he's a bit older). Also he should just plain change his family name, and maybe take the one he had in his previous life, since then his parents actually loved him..
Also, he can have a healthy relationship w/ his little sister, when he becomes independent first, so he doesn't have to permanently abandon her, even if he left the family (or was kicked out). Though it would take some years to see her again I guess.
All in all, I don't think a setting like this is bad per se. It's the way it's handled, and how MC reacts to his shitty human garbage parents... There should always be self-respect behind every decision. There's a limit how much shit a person should take from their parents, and I think we're already well over that limit on the MC's case.