And since he has Memory AND Body, at Level 5, there's a chance that he could potentially Copy the Abilities of Superhumans & Monsters OUTSIDE of the Dream Realm.
I'm pretty sure Syla could only do it in the Dream Realm, then again I don't think that was EXPLICITLY stated, so I could be completely wrong, but we do know that she was DEFINITELY stronger within that Realm as opposed to on Earth.
The MC might even be able to retain the Abilities for 'longer', and even mix match them. Though again, that's all Theoretical, and DEFINITELY End Game of it was ever implemented. The MC's just cracked. Besides having both Body and Memory, two Traits that are closest together AND Apostle Traits, he also has the potential to maybe...'strike a deal' with an Arbiter? Depending on how that whole process works. He's got the most Potential, fuck whatever Ella was saying with Jake, at the end of the day, Two Traits at Level 5 is better than one, if EVERYONE was capped at the same Level, we will still always have the advantage in having more ways to fuck with people.
As of right now, we can guess at Level 5 he'll probably be able to use Body and Memory at their Maximum Capacity, but with an Arbiter 'deal', there's a chance he might be able to get an even Stronger Trait that is a Combination of the two. I can't imagine the Arbiter is just a simple Power Up when compared to the 3rd and 4th, that would kinda be dumb in my eyes, considering the Apostles themselves seem to be able to use Both Traits anyways. And while I know we've already seen what the Arbiter could do in our Body, keep in mind we were an 'incomplete' Vessel, there's still a chance that a Fully Maxed Out Arbiter is an absurd freak of nature like I predict, housing a new Trait that combines the Lower two.