If you know how to use a scope such as the ones being mentioned correctly, mental math is absolutely unnecessary regardless of the angular units chosen. Period. Full Stop.
The argument about fractions is false. Fractions are difficult when dealing with different denominators. When was the last time you saw an MOA scope that used different denominators within its own windage and elevation adjustments? In any event, see my previous comment about math.
When it comes to MOA vs IPHY, can you name one single time you've ever seen that be an issue in practice? Me neither.
I chose mils for my precision rifle scopes yet could have chosen MOA and be equally as effective. My hunting scope, Aimpoints, and AR LPVO all adjust in MOA and cause me no issues.
I'm unsure why the attitude is necessary. Full stop.

I agree with you, except for the following issues.
MOA is a non-issue unless your spotter uses "MOA" but gives you wind calls in "estimated inches" rather than MOA (I HAVE had that issue before, years ago when I was still using Leupy mil/moa scopes). Or when most everyone around you is using MRAD and you're using MOA. Then you have to convert whatever calls your spotter is giving you, though I suppose this issue works both ways. But the first issue is one I still hear occasionally from those who haven't learned that, yes, it's an angular measurement and should be used as such. If your group of shooters knows not to compare things to inches, etc., then you won't have any problems.
Also, I, personally, have not run into the MOA/IPHY issue because I use MRAD, as does almost every other shooter in our club. Non-issue for me. Frank seems to think that the shooter MOA/true MOA/IPHY is still an issue, as many are unaware of the difference and how to correct for it in their ballistic software, or even that they have to correct for it in the first place.
The comment about fractions may have been poorly worded and technically incorrect, but to my mind, using a decimal is more natural. However, I'll concede that you're correct about it being no factor provided everyone is on the same page when giving you corrections. See my post above.
My MAIN point is that both reticles will work just as well as the other, as long as you educate yourself on them. But for most folks, a base ten system is more natural, as it's what we use in money, and what the rest of the world uses for pretty much every other form of measurement (I wish we did as well)!