Quite an interesting theory.
I also have one of my own.
I believe that the word "perfect" meant that MC can steal powers, which is the ultimate evolutionary ability. Let's not forget that she used this word only after we revealed to her that we had "borrowed" the abilities / characteristics of certain animals. In addition, we have proof that it works also on super humans, because we gained some powers of the guy who made zombies out of black slime.
Ella has very similar abilities to MC but there are significant differences. Ella can change her body without restriction and at will. Her starting point is much higher than the one MC had. Unfortunately, her body is also her limitation. Although she could turn into a snake, for example, she would not have poisonous teeth. Her current form would only change shape to snake. MC is able to turn into a full-fledged snake, which would be 100% the same as the original. Unfortunately, he is limited in that he would first need to find such a snake and touch it. So take the ability to make perfect copies (+ combine the characteristics of different copies) and the ability to copy / steal other people's power, and here you have something every superhuman would love to have.
I also believe that Ella has the ability to absorb dead superhumans. That's why she gives away so many pills and tries to make her "childrens" reach their full potential. But given her behavior, I conclude that she is only able to absorb your current level of power, and that absorbed power inside her no longer evolves. Therefore, she needs only strongest individuals with the most useful abilities.
And regarding Natural and Artificial Evolutions...
I believe that artificial evolution is just an improvement on your current abilities. Something like +200% to all current stats and abilities. But natural evolution is something completely different. Not only will you get a general power boost, but there will probably be some changes and/or new abilities. In addition, the change is much more personal and adapts to your needs.
P.S.
Serum for artificial evolution is most likely created by processing monsters.
I'm pretty sure it's obvious, and everyone knows, that the serums are created from Monster essence. That's why they wanted the Fairy "corpse".
As for your "perfect" part, it's fully compatible with what I said about his power being potentially a new "Authority" type thing. If he reaches Lvl 5, Naturally, it could potentially evolve into it a higher power form and allow him to ascend into a Numbered lvl being or be on par with them.
Though, I personally don't think he can steal other's monster abilities, yet. From all his encounters with Superhumans and monsters, he mostly just devour their power and converts it into more for himself. He doesn't gain their abilities(check the Danica kill route) as it would ruin his purity. Could his ability evolve further with Evolution to do it? Sure but right now it doesn't do it. I'll have to also recheck that Danica scene.
Natural vs Artificial is pretty straightforward, like you said. Artificial uses a mixture of serums to forcefully boost themselves higher but at the cost of their abilities forming a plateau. In a sense, they contaminate themselves with ungodly amounts of different Monster essences. Natural is just staying pure with your own and evolving while being under your monster parent influence(not always the case).
We have a few examples of Artificial vs Natural Superhumans. Klaus vs MC and Ella vs Clark and Alexis.
Klaus case had him being back and forth with MC, in their final fight, before they both evolved. When it did happen the MC dominated him fully.
Clark and Alexis weren't much of a threat to Ella in the park. I'm assuming those 2 were peak Evo lvl 3 at the time but when Alexis and Clark took the serum they jumped to her lvl(4) and Ella started to struggle. Go later to the Hero HQ scene and even at Lvl 5 they weren't much threat for Ella at, most likely, a higher power lvl 4.
Anyway, that's about it for my takes, at the moment. I'm mostly holding off until I play the update as I'm sure there's going to be a lot of new details coming from Numbered Monsters, Evolution and more into what Ella's trying to do.