I have a Nazgul in my Schecter (tuned down a half-step) and I love it. It's vicious, with a great mid body, and it chugs like nothing on earth. It is def a metal rhythm pickup, though, and that's what I use it for. For cleans, leads, or anything else, the Sentient does the job fine. I hope you're able to get this wiring issue sorted out!
It's always good to know when to say when.
As for the Nazgul's tone, I've never had one, but I never really understand how a pickup can be too harsh in the highs or upper mids because those are such easy things to adjust after the fact, like with boost/od pedals and of course the amp itself,,,,,,,,granted there can sometimes be a combination of all the "wrong" elements in one's rig, but that's not the norm IME.
(pickups in general, not talking about the Nazgul here)
The low-end's character is where I find things to get harder to dial-in or out, although dialing-out too much lows is easy as long as they are still as percussive as desired.
If the lows are just too spongy then it's hard to find anything that will take them into the stiff and percussive zone. You can "tighten" them but that usually means just reducing the lows in general, not really changing their character.
I'll be curious to hear your opinions on it in the hard rock context once it's rewired.
Some people say it's muffled and dark but every demo/comparison I watched sounded clear and percussive, which makes more sense anyways being it's designed to be good at low tunings with high gain.
I still have the Nazgul, like I said, imho it sounds great but then it wears on me for some reason. I tell you this as well, may sound crazy but if your intonation or tuning is off just the smallest amount, the Naz will let you know more than any other pickup I have yet to try. That being said, it really does come into its on when tuned down. I keep that guitar down half step and it seems to love the lower tunings