Howdy Cincinnati, 'morning, all!
Cincinnati, I am certainly no expert either but, one thing I've learned (through some hard le$$ons) is that Japanese maples root systems need AERATION. This equates to sorta the opposite of manure - think of a soil composition of roughly:
1/4 SHARP pea gravel (most often quickest source is chicken grit from your local feed & grain store)
1/4 pine bark FINES (not to be confused with pine bark mulch although my last JM planting I got by with the MINI pine bark "nuggets" and I just picked out the bigger biggest "clunks" of bark)
1/4 sphagnum peat
1/4 soil (not manure, not clay, not sand but soil that, for lack of a better analogy, when you squeeze a fistful of it in your hand it stays clumped for a moment but then starts to separate and crumble)
A lot of people refer to soil for JM's and other plants that like relatively "dry toes" "GRITTY MIX" and the recipe I use a mass of us actually got from a guy named "Al" and so you may hear people refer to, lAl's Gritty Mix"
Aeration and drainage is so important that last planting I mention I actually went 1/4 everything and the last 25% I used Turface, essentially fine bits of clay which have been fired to some insanely high degree of heat that makes it rock hard and yet it absorbs and holds water! It is used on athletic fields and you can get big bags of it at turf shops like SiteOne (I believe used to be John Deere Landscaping stores), etc.: https://www.turface.com/find-a-distributor I think I used the MVP but, the pieces should be large enough to not be considered close to sand and large enough to not be considered gravel. Maybe easiest way to put it is size of the Turface particles should be smaller than the chicken grit.
One question bouncing around my head is, "What was the soil like at your parents', where the tree was doing so good for 4 years."
You have a couple options but, I am fairly confident they all involve amending the soil. Since we're coming up on the hottest, driest part of the year, "rescuing" any plant can be a tricky proposition with it out in full exposure. It looks as if the root system of your tree may be too big for you to put it in a pot with and move it to a partial til, say, September but, that may just not be practical for you.
At the very least, I'd consider getting yourself at least 4 10lb bags of chicken grit (you want particles about the size of pencil erasers or slightly bigger and THE SHARPER THE EDGES THE BETTER); 2 or 3 bags of the finest pine bark ("mini nuggets") you can get and if you can't source Turface then even several bags of perlite. I wouldn't think you would need any planting soil as I suspect the soil you have there will be fine, once you mix it with equal amounts of the chicken grit, pine bark fines and Turface or perlite. (OTOH, if that area is pure clay or sand then, yeah, score a couple bags of generic planting soil as well.
Dig that little beauty up, create a hole as deep as and twice the diameter of the root ball and get to mixing! If you are mixing and thinking, "Geez, this is almost going to be "too dry" for the plant to retain any moisture" you've probably got it right. When you replant the tree make sure it SITS HIGHER than the rest of the planting area. Then give it a good 2-3" layer of regular pine bark (pine bark actually contains lignins that prevent their breaking down as quickly as many other "bark" type mulches)
Depending upon what you see once you get the roots out of the ground, you may want to either prune some of the finer roots back and at the very least make sure they are not "clumped" together (which they tend to do when they stay wet (and heavy % of manure turns to an underground "glue" :-(
As I type all this I recall ecks in Texas mentioning "the cost of the cure may make it not worthwhile" (or something along those lines) so, only you can decide if a replant is practical or not but, in any event, I hope all this is a bad memory asap and that everyone enjoys that tree for many, many years to come!
Edit: on looking at the picks again, some light (as in very light) pruning of the ends of the longer ("wispier") branches may also aid the plant in recovering. I know the consensus has shifted against sealing pruning cuts but, I am fairly certain most would agree that Japanese maples, and especially already stressed specimens, are an exception to the "don't seal prune cuts" rule. Therefore, I'd dab a finger tip of Elmer's glue on the ends of any branches I pruned back.
Best o' Success!
Another Edit (geez!): it can only help (a lot!) if you can also get a nice sized bag of bone meal and incorporate that into the soil as you backfill directly around the edges of the existing root mass (I can't say enough about using bone meal when I do transplants!