The game pretty much states this why do you think Ella gave him the the lighting monster's pill because lik his brother Met his compatibility is higher to a lower level monster whereas Alice and Mc are highly compatible to apostles even though Alice isn't an apostle spawn she has very high compatibility with the Ether .Michael pretty much forced his way through sheer will and skill to get a higher tier power and parent.
I don't think monster compatibility works like that. The game only ever talks about two types of compatibility: general compatibility, and compatibility with specific traits.
General compatibility is how compatible someone is with getting powers in general, and shouldn't be influenced by the powers you receive necessarily. This is supported by Ella saying that Emily has higher general compatibility than both her and MC, but she doesn't know what monster parent would specifically fit her. If this was about how strong the monster parent was, you'd think Ella would've definitely just chosen one of the apostles to be Emily's monster parent.
Another point is that MC's dad was perfectly compatible with body but had atrocious general compatibility, so he couldn't get any power without monsterfying.
Trait compatibility, meanwhile, is self-explanatory. It is the reason MC isn't a perfect mix between body and memory, and a much more likely candidate for why Ella thought the Leigong fit Michael better, as we know it is genetic, or at least related to your heritage in some way, and not (entirely, if at all) mental, as well as can change (though the circumstances might need to be extraordinary), as Syla's formerly perfect compatibility with memory decreased. This I see being lower for Michael, but Leigong is still mostly a power-based monster, so it shouldn't be low in any meaningful capacity.