Definitely would do an aftermarket heavy barrel.
I've heard folks have issues with the quick barrel statement on the DMR (not holding tightly and causing flyers).
With your Swiss what MOA would you be getting if you weren't using the bipod? I'm not a fan of the whole integrated bipod system.
Doesn't have to be a heavy barrel to shoot well, just has to be a quality barrel that has been properly stress relieved.
Mostly excuses from my experience with the ACR. The system uses a ratchet so it can't come loose once it's tightened. This is the second ACR I've owned, I traded a black rifle for the FDE one and I've never had a barrel come loose on either of them.
Hard to say what it's actually capable of but with American Eagle black box 55gr FMJ it was 3-4 moa if I remember correctly. In comparison what I actually remember more than what size the groups were was that it was slightly worse than the ACR but to be fair the SA has a rack grade (Swiss rack grade) barrel and my ACR's have all had aftermarket quality barrels (I've owned 4 non restricted 223 barrels for the ACR plus my 300BLK and 6.8SPC barrels). I've never even shot an ACR with the factory barrel, lol.
Unfortunately I had my Swiss Arms green, my ACR, and an HK SL8-4 with HERA Arms lower and ACR folding stock all at the same time and rather than do a good ammo test on all of them I decided the multi-cal and superior ergonomics of the ACR was what I wanted most.
If accuracy is your goal and all you want is 223 then the HK SL8 with a HERA lower is the best rifle out there. It's muzzle heavy but nothing can touch the Lothar Walther barrel they put in them. I've owned three of them over the years, one was completely stock, the second was the HERA lower one and I recently had a G36 conversion one for a short time. All of them shot extremely well and the first two were capable of sub moa with handloads and premium match ammo, the last one probably was the same but I sold it before I had a chance to do much testing with it. I have also seen a couple other SL8's owned by friends shoot sub moa.
The ACR is capable of great things with the right barrel but it will cost you around $1000 to get a good barrel for it. With a regular quality barrel it's still more accurate than most other options but you won't be seeing much for consistent sub moa unless you spend the coin.
If I was shopping for a non restricted 223 and I wanted it to be accurate and light weight I would buy a Modern Varmint with the carbon wrapped barrel. As far as I'm concerned it's a toss up between it and the ACR with each of them having minor advantages over the other depending on what you are looking at. I'm keeping my ACR because I have my 300BLK conversion for it and the MV doesn't offer that and I can't buy an upper from them without a barrel so I can install my own. As it is now I'd have to buy a complete second upper and then sell the barrel it came with and install my 300BLK barrel to get what I want and it would cost me more money than what I can sell the ACR for.
