Harmonically, DI will consistently be better shooters. Not too many piston guns out there that keep up with DI precision rifles.
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There are factory piston ARs that can shoot sub-moa consistently at 100m with a good shooter on the trigger and match ammo If you care that much about tenths of an MOA, a semi-auto isn't going to be used in the first place
In the case of the HK417, it's plenty accurate - it was selected by the Army as the next Squad Designated Marksman Rifle and given the M110A1 designation under the CSASS program, replacing the Knights SR-25
The MR762 would be "worth it" if they came with a chrome lined barrel, adjustable gas block, normal takedown and pivot pins, and ambi controls like the actual G28, M110A1, or some variants of the HK417.