Far superior is quite a stretch.
Not in my experience.
How many threads have been started on this site with guys having broken ejectors, broken op rods, broken buffers just after break in, and a pile of other issues?
I will say that Wolverine has been doing a fantastic job of taking care of everyone's broken rifles but they shouldn't have to be doing this much if the rifle was just built right from the beginning. The people in Rob Arms QC department should all be let go for letting some of the rifles through that have failed after very few rounds.
I own an ACR and have shot 4 or 5 XCR-L's and an XCR-M ranging from when they were first released to the latest model before the keymod one. None of them compare to the quality of the ACR and the accuracy of the XCR can't even come close.
The XCR is a good rifle but the QC is poor and the design of the barrel retention is stupid and is why the rifles don't group well. The ACR is a great rifle with excellent build quality and good QC.
The coatings on the ACR are superior as well, the Nitriding is self lubricating and they claim the rifle needs little to no lube to run for thousands of rounds.
The only thing the OP needs to look at to make his decision is his budget. If you can afford the ACR and can afford to have it converted to non restricted then it is the clear choice.
If you buy a used ACR for $2200-$2500 then add the cost of a non restricted barrel from Dlask ($550) you are looking at $2750-$2950 depending how good of a deal you got on your used rifle. I picked up mine for $2200 with a Geissele super ACR trigger then found a used Herron Arms conversion barrel. After selling the 12 inch barrel mine came with I was into it for about $2500 before I picked up the 6.8SPC barrel and 300 Blackout barrel.
The only advantage I see the XCR having is the factory support for caliber conversions. Both of mine are custom built barrels but I paid less than the $700 the XCR conversions cost.