It's hard to suggest a catch-all pursuiter for ghosts because as you said, between the possibilities of ghost and fighting coverage, as well as scalds and will-o-wisp and HP fire, scizor, tyranitar, and bisharp don't 100% win against all of Aegislash, Gengar, Jellicent, Chandelure, and Sableye. Bisharp can be OHKOd by them so there's a guessing game between sucker punch or pursuit. Scizor is robust but fears fire coverage and burns and has an iffy fight against Aegis. Tyranitar is also bulky but again falls to fighting moves. Weavile is faster than gengar and guarantees the OHKO but can't quite get through Aegislash with a mere pursuit. Metagross can't have his attack lowered by Aegislash but can be OHKO'd by life orb gengar and shadow plate Aegis. These pokemon are great choices if you can scout the ghost's set first and if you play carefully, but you can't easily accomplish what you are trying to do.
I've looked over every possibility from Scizor to Contrary Bisharp to Defiant Thundurus-I and the plain fact is there is no pursuiter that can guarantee a KO on Aegislash by only using pursuit. You will have to wear it down to ~50% if you want something like scizor or bisharp to kill it, or, you have to get lucky and it stays in while you hit it with a strong Knock Off without getting your attack lowered. Gengar is less problematic because of his sheer frailty, even scarf metagross can kill him with just a pursuit. Sableye is also there, and is also tough to kill unless your pursuiter has a Lum Berry or something.
You will need more than one pokemon to guaranteed clear out Aegislash, Gengar, and Sableye for a Mienshao sweep unless you can always guess correctly when to use Pursuit and when to use Sucker Punch and when to use Knock Off with Bisharp.