Japanese maples don't like wet feet. It looks like you maybe have it in standard potting soil. They do better in a more porous soil that doesn't hold a ton of water. With the hot weather we're having lately, you may feel inclined to water the tree constantly, but you have to let it dry out to some degree before watering again. For a plant that's in standard potting soil, it's better to give it a good soaking, then just leave it alone until the top 3 or 4 inches of soil have dried out before giving it any more water. Also, once you have a bunch of leaves dropping off like you've got, then that's less water in the soil being used by the tree, so overwatering becomes a real danger.
It also seems that since you did a trunk chop earlier this year, followed by heavy pruning, that has overstressed the tree. When you said that the tree "stalled" after you reduced watering and moved it to a shady location, it was doing this because it just took some major hits and needed ample time to recover. Neem oil is great stuff when used in appropriate situations, but I wouldn't hose down a heavily stressed tree with it. I would just check it daily for any pests and remove them manually. They're probably showing up because the tree is not doing well. JMs can take some heavy pruning when they're healthy, but you can't cut all the new growth on the branches. You need to leave some sets of the new leaves behind when pruning. Like if a branch spits out 5 or 6 new sets of leaves in the spring, you can get away with trimming back 2 or 3. Don't cut all of them.
I'd throttle back on the water, and put this tree in a place where it gets no more than 2-3 hours of morning sun, followed by shade for the rest of the day. Leave it like this until it recovers, then a little more sun is OK. We're about to get into the hottest time of the year, and most Japanese maples don't like tons of sun as it is, with a few exceptions. A sick tree REALLY doesn't want to get a lot of sun because it can't handle the stress. I also would not do any more work on it this year. Right now, it's not a bonsai that's in danger of dying. It's a standard tree that's in danger of dying, so just focus on saving it as a tree for right now. Then, if it recovers fully, I would repot it next spring into a soil mix that is more porous and doesn't hold as much water. If you want to leave it in a pot as opposed to putting it in the ground to grow out, you can use a soil mix that is 2 parts standard potting soil, 2 parts "in-ground" tree and shrub soil, and 1 part sand. The "in-ground" soil doesn't hold as much water as standard potting soil, and this combined with the sand makes it harder to overwater potted plants. I've had success with this mixture for a long time for trees that are growing out in nursery pots and for many of my porch and patio trees that are in large decorative pots. It holds enough moisture so that I'm not watering every single day, but it dries out fast enough to keep the roots from getting soggy.
Japanese maples are beautiful and very rewarding, but often finnicky and/or fragile trees. Good luck and keep us posted!
