Funny rules, but they do make the MC OP.
* magic power is dictated by lineage (genetics, basically), talent and effort.
* This guy in his first life obviously had talent (his analytical skills in particular) and very likely put in the effort.
* Got reincarnated as royalty, even if low on the inheritance list.
* MC is then maxed out in all three requirements at the time of his second birth.
I do see a few problems with such "convenient" rules that automatically make nobles stronger than commoners... but it's consistent so far.
Overall a basic manga with OP character, not really original. Just good enough as a filler between the updates of the good ones out there.