Kairaku I don't see how. There's nothing involved in any of that that's contradictory or requires sacrificing personality. The only real affect it would have on personality is requiring you to be a Paladin, so you've at least got to be religious, and that's hardly unreal, and a preference for being the one protecting others rather than the one harming others. Which could, but doesn't necessarily have to tie into the religious element.
Focused on defending people over hurting people? Not terribly unrealistic. Takes pains to ensure they survive doing so? Also, not especially unrealistic. Gets pretty good at doing this through significant amounts of practice? Yeah, seems legit.
And none of that, not a single bit of it, in any way inhibits you from having a believable and well-realized character outside of their mechanical role. Hell, if you really get into it, the religious angle can go a long way to helping with that.