we might assume that the two-faced Gamzee is himself composed of “human” and “animal” half, and that by absorbing “half a Gamzee”, Caliborn inherited only the animalistic shadow-self; a fitting fate for a character who is master of chucklevoodoos - the art of manipulating these subconscious shadow-forms - and a character who is, in all the ways that matter, the Incredible Hulk.
but it might also be argued that Caliborn, too, is simply one-half of a person, having expunged his sister personality? and that by putting two halves together, we still end up with a being who is one full half Gamzee. and if this is the case, is it not just as likely Lord English is a submissive Caliborn half attached to a dominant Gamzee half?
or perhaps it is the point that Lord English is composed entirely of two shadows with no real “face”; he is the Incredible Hulk, but one without a Bruce Banner: the very concept of the shadow self made incarnate. in which case the question of whether he “is Caliborn” or “is Gamzee” is entirely secondary to the fact that he “isn’t” Andrew Hussie, having been constructed from pieces of the author rearranged into the shape of an anti-author. (read: Lord English is God’s Hulk)