Uh, re read what you wrote and do the math.
4 moa of potential error in you, and 4 moa of potential error in the rifle adds up to 8 moa.
4 moa of potential error in you, and 1 moa of potential error in the rifle adds up to 5 moa.
This.
Now add in a bit of distance, lets say 300m which is medium distance for a modern 556 rifle.
Our 8 MOA translates into a 24" pattern. A pattern that large offers misses.
But real world has more than just sandbagged bench Vs offhand standing. Overlooked is prone, squatting/kneeling, standing but using a marksman's sling for stability.
I have no dog in this debate, I don't own either of these products. But...XCR has been out for many years, not adopted by any military or paramilitary unit AFAIK. And if low-mileage civilian hobbyists are complaining about the occasional parts breakages, this does not inspire confidence for a new buyer.
The ACR is new. So new, that its track record, and reputation are not old enough to be sure if it can truly be trusted. But at least a small sample of units are being field tested by specops operators...no idea what they think of them though. And one country has adopted it for a small number of designated marksmen (which becomes the Canadian Non Restricted variant due to longer barrel from factory). But...both are such small numbers as to not really be any further ahead than the XCR.
Contrast those against the decade of urban warfare seen by Tavor users in Israel, Lebanon ops, and routine patrols in disputed territories. Its proven itself massively. No its no accuracy machine, but it is proven for very harsh conditions, very high mileage, handy for vehicle and CQB urban. Adopted by India special forces, Guatemalan Navy special forces, now produced by Taurus under license for use by Brazilian special forces, Colombian special forces army and police, Azerbaijan specops, Georgian army bought 20,000 units, Thailand bought 58,000 units, Ukraine was about to start manufacturing setup for Tavors in 5.45 cartridge though I'm sure that's in limbo now Putin is seizing the country...oh and Vietnam is also buying Tavors for specops marines and navy. Anyway, with only a decade on the market, the Tavor is being used by quite a lot of military units, speops units, around the world.
We could then look at the two decades for the Swiss Arms, in use by an awful lot of specops hostage rescue teams. And several armies.
Yet the XCR has been around almost as long as the Tavor and...well, I think the users list speaks for itself.
Could the XCR and ACR prove themselves in future? Absolutely they might. But its not a guarantee. Reputation comes from many early users reporting good results. But even if your product is good, if sales are low, you may not generate much reputation statements.