In response to your quote from the trailer:
"We found him. He tried to take over. We exiled/imprisoned him..."
That actually fits the backstory of Garth.
The race of "shape-shifters" gifted him with their ability to change form because he was so gravely injured, and could have in some way altered him mentally. He ended up turning on them and wanted to destroy them. Naturally his officers turned on him and Garth was inevitably imprisoned/exiled and later deemed insane by Starfleet.
So IMO this quote from the trailer more fits Garth...not Khan.
That quote was not from the trailer. That was a generalized idea from me of how to handle the Khan backstory in film.
And the shapeshifters never gave Garth the sort of "supersoldier" attirbutes that the trailer character displays. Garth was not a one-man weapon as the trailer character is said to be.