I always thought of Necromancy as a field of Magic that requires a lot of groundwork, rituals, power and questionable magics, and a general need to stay stationary when you're doing the ground work.

I doubt that Harry would, 1, be capable of doing anything before Voldemort absolutely demolished him due to Harry placing a lot of faith in an esoteric field of Magic that only serves to disrupt the natural order of nature and magic. And 2, Harry has no real use for it besides some very deep-seeded, maybe, kinda, goal to resurrect parents he never knew. The idea that Harry would try so hard for people he doesn't know, nor does he appear to want to know aside from the odd staring at a picture or something is quite odd.

If we change his very nature, he isn't Harry anymore, you'd have a necromancer OC with the name Harry Potter.