These are all good ideas and I practice them with my own horses, except the treat part. I give treats as a surprise maybe twice a week after end of any training session. Another thing you can try is just turning your horse out in the round pen, let him run around by himself without any direction from you, then get him to face you and catch him weather he walks to the center or not. Halter him, rub his neck a few times, then take it off and walk away leaving him to do what he pleases. If he follows you, definitely acknowledge by rubbing then playfully chase him off to go run. Do this a couple more times then put him away. He’ll soon come to realize that you catching him may mean nothing but a loving reward. I’ve done this many times with my four horses and three will run to meet me while the other makes me come to him but waits nonetheless. It’s def worth a try. If I made you go to the store every time I asked you get dressed, you wouldn’t want to get dressed anymore. I do the same with saddling. We may ride, and we may not. This way nothing is predictable and it keeps up the curiosity. Good luck! I understand the frustration. I volunteered for a therapeutic riding center where this one horse had me chase him all over the pasture. When he was done having his fun and had me halfway out in the field, he would happily trot up to the gate and wait for me there. Oh that horse!
"A horse is the mirror to your soul...and sometimes, you may not like what you see in the mirror"-Buck Brannaman