IMO, superhumans who used Xanthe's serum to evolve to Level 5 aren't as strong as a naturally evolved one. They're more like a pseudo or false Level 5. (That's my theory anyway).
I would say Syla and the rest of the Chosen can easily defeat a false Level 5 but a naturally evolve one is a different story.
Judging by the information we now know, it's likely true that a superhuman artificially achieved Level 5 won't be as strong as a naturally achieved Level 5. Clark mentions that the busted trio all had requirements they needed to meet to achieve their fifth evolutions, some of them dangerous. With this in mind, it's very obvious that Level 5 is supposed to be achieved via completing rites. It's also shown that completing these rites can give permanent buffs to a superhuman. Multiple characters either implicitly or explicitly got something - or will likely get something in the future - from performing certain feats. Ella gained her eyes after performing her some unknown rite. The MC gained semi-sapience and augmented capabilities in his liquid state after treading the paths of god. Michael's current goal is to gain a permanent evolution trance through performing rites.
Seeing this, I'm of the opinion that whilst a Level 5 made via Xanthe's serum might theoretically be able to match a natural one in Monster Power with time and training, they'll always fall short in the potency and versatility of their powers due to irreversibly handicapping their potential.
On a side-note, I also think fumbling rites is the thing that makes your Apostle decide you're a failure. Ella's third evolution was pretty obviously a rite in hindsight, one that would have likely given her full access to the Memory trait if she didn't deliberately fail herself to save Christie considering the fact that she was specifically looking for "minds" and "memories" in her trance. Her price for this was being dubbed a failure. And I may be reaching, but I think Jake vs MC was supposed to be a rite for Jake. Even though he missed his Level 2 evolution trance, the Authority still thought he was worth something. It whispered to Jake, pushing him to exert his powers on everyone and everything. It even seemed to imply it would remove his weakness of getting hit with power backlash if he tried a regular order on a stronger opponent, which I believe would have been a rite completion reward because third evolutions don't typically remove weaknesses like that, just give greater control or buff you to hell and back. Afterwards, Jake is punished with repeated dreams of torture for being a failure, which considering they tried to jump you for winning if you eat Jake is probably in character for the Authority.
