It’s not even about figuring drop in your head. Even if both shooters need to look at their DOPE, base-10 is easier to manage.
If your DOPE says 6.43 MOA, you’re going to dial to “6” and then think “how many 1/4 MOA clicks is 0.43?” You’ll then round up to 0.5 and dial two more clicks. If your DOPE is 2.3 mrad, you’ll dial to the “2” and then add 3 clicks. Simple. If your DOPE is 17.65 MOA, you’ll dial one 15-MOA revolutuon and then think about adding 2.65 MOA, dial to the “2,” round up to 0.75, and add 3 clicks. With mrad, if your DOPE is 12.8 mrad, you’ll dial one 10-mrad revolution, dial to the “2,” and add 8 clicks (or dial to “3” and take away 2 clicks). Notice that with mrad you’re not rounding numbers in your head. Under stress and time pressure, simpler is better.