I'm with you on not liking the blunt cut.
I pull just a few hairs at a time. Mostly from the underside. If I want less length, I pull the longest ones. If I simply want to thin the mane, I pull some of the longest, and many of the medium length ones.
It's tedious. And if the mane needs a lot of thinning, I break the task into two sessions in case the horse tires of it.
A couple horses I've done had really "tight" roots. For those I taped my index finger with sports tape. Tried vet wrap/coban, but that did not hold up as well.
Good luck. I bet he looks great after you finish, and feels a lot cooler under all that mane.