Not to be confused with the Soul realm crewmate
The Mega-crewmate is not really an entity. Its more like an concept of how strong an average crewmate could go (excluding the Soul realm crewmates). Only chosen crewmates could go higher than this point. In first place, chosen crewmates could reach this power, but the chosen ones of the chosen ones could go way beyond this point. Its a bit weird, but thats what this entity concept its like.
To make you know how strong these entities could go, they could easily wipe off the Patriachogus and maybe the entire impostors species, but thats not confirmed.
Like i said before, this is an concept, so its not confirmed to be real. Its probable that this "concept" could have more or less power.