User blog comment:PaulLevesque555/Mym/@comment-25848535-20190613030246/@comment-32751919-20190613085206

TL;DR His role would be too similar to those people, especially Jeanne. Also Higashiguchi want offensive-focused grey morality character than defensive-focused saintly character.

That said, I think his NP that grant him invincibility also the reason as well, even it main reason while compare to the first two, but still count. (Author also aware of it.)