Ah, well, I hate to defend this story on any aspect; but from the outset the twist to this story has been that almost no one in this fictional world can work with more than one magic (and the MC alone can work with
all forms).
[Editted to correct an error noted by
@DeadKinginHell.]
Though of course, nevermind that he saved a noble's daughter and clearly displayed his ability to use a lot of different magic elements and somehow that news never spread and nobody went to look for this mystical being who could use multiple elements and a bunch of other conveniences that really just are just big holes in the foundation of the story that was never addressed or properly filled or covered over with other worldbuilding to at least provide some equivalent of swiss cheese defense where at least there's more explanation of the world building that provides some established alternative reasons as to why nothing came out of it.
So hey, you don't really need to defend this story much. It is trashy and pretty bland, but it can still be enjoyed for the bland trashy thing it is. Y'know, like when you have a craving for McNuggets. It's not good for you, it's pretty damn trash, but hey, when the craving hits.