With Ella specifically we have 2 reasonable guesses on how she "screwed up". First being the failed ritual during the school massacre and second by simply not being chosen by the Eye. Though the second one is more of a guess than the first.There is. Since Superhumans are constantly adapting to both the power and their surroundings and thus to how they use their power, it stands to reason that you can screw up your progress, like Ella did.
We are not sure of the exact mechanism, but with the trials, there seems to be a 'right' path and while that doesn't necessitate a 'wrong' path, it implies that Superhumans can adapt in ways their ancestors would find undesirable.
It's especially the talk that Superhumans have the potential to outgrow their monster parent. To me all of that is just a lot of implications to talk around the actual situation.
But back to the main topic: None of what you mentioned really effects the serum since it's just a refined version of a known way to force evolution, just like how the MC almost forced an evolution at level 1 when he tried to see how big he could grow. The main probable ways to "screw up your progress" is either to fail trials or possibly go against your intended purpose. But considering the 3 Captains the latter may not be a factor or they shouldn't have become as powerful as they are.
In fact the trials and power progression for each superhuman may be outside of the Apostles control, they just know what needs to be done to pass the trials and if you have someone else (like Henri) who can tell you what your trials are then the Apostles input is no longer needed.
The word "trial" may just be a misnomer, they are only called that because they are usually tasks given by the Apostles and what they are actually just ways to progress your power that may be unintuitive, like how the MC needed to learn to shapeshift objects or make metal. Michael absorbing a planets worth of heat probably isn't something he would normally think to do for example.
As for potential to outgrow your monster parent: That may or may not include Apsotles. I say may because the 7th/Darkness/Lord of Dark seem to have "usurped" the title. In any other cases, well monsters can't really get stronger outside of rare mutations where a superhuman at level 3 and up have a theoretically limitless power ceiling as far as we know.
Based on a early-ish conversation with The Eye it may be either eating as many strong people as possible or forming as many bonds with people as possible.Yeah, but as she herslef said, everyone searching for their own ways to empower themselves, rather than just keep gaining power via training is the way to go, the Captains most definitely did that on a way that would make sense for their powers, MC is doing that too, eating memories and samples of powerful monsters to keep improving his body and transformations, he's on the right path, but given how 'easy' is for him to diverge in path thanks to the nature of his powers, I suspect that he need to go to a larger extreme to branch his powers in the manner the Captains and Nico did. I mean, Nyx has a ton of differences with the Monster that is suspected to be her Sire, Lucius is confirmed to have warped his powers in some way thanks to corruption, and finally Malik has a sixth sense to tell if a Monster has killed a human or not, despite being mainly a Pyromancer.
There is a decent in-universe reason for it I can see: Nico (and her power) is practically unreplaceable and core to HERO operation while the "Do Nothing Duo" is... Not. Alexis and Clark getting the finished prototype, as an emergency plan when going after Ella, before the designated chauffeur of HERO is a solid enough reason.Oh yeah I know. I meant he'd still have to keep impressing Xanthe to get the serum sooner than later since Xanthe gives it out pretty slowly. He's been very impressed with MC so far so MC is probably on the shortlist for it. But even Nico had to wait a while and she's bordering on being as important to HERO as Zack. Alexis and Clark getting it before Nico was dramatic for a showdown against Ella, but it's almost certainly just one of those early writing choices that doesn't quite mesh well with how the story has developed since.
Though Clark really has been putting the work in lately, without him it would probably be much harder if not practically unfeasible to hit monster worlds like Malik and Bernhardt is doing.