The reason why the M1 mortar is regarded as a hand me down version is probably not the AoE that were THAT much worse, but all the combinations of small downgrades.
Worse AoE
5 less range
And most importantly: It screws up all USF timings.
Building the mortar that early means giving up a Rifle squad, which you'll dearly need against Axis spewing out main lines at this time. Alternatively, it delays the officer and LV, so also not a great option. Worse AoE gives you a worse performance overall, and the 5 less range ensures that you're more likely to get hit back by artillery even in the early game. If my math is not mistaken, moving those 5 meters in means that an OST mortar could be laterally displaced compared to the target by roughly 28 meters left and right (so 56 meters in total) and still be able to hit you. You're also more likely to constantly needing to move the mortar to make the best out of it, in a faction that is fairly micro heavy.
Also, is the cost difference really only 10 MP as coh2.win states? I somehow thought it would be more.
As much as I respect his fortitude and decision and tenacity to create such simulations, they serve no real purpose. On paper they look nice and all, but the amount of extra, beneficial information they give you is nil. Mainly because there is no standard empirical method with which you will measure. It's a game with a large amount of variables/parameters, and trying to fit it to some model is... well. Not really necessary. Not to mention impossible. As nice as it looks, it's just a bunch of simple equations fitted to some data model, which was taken from the seralia stats. Not really telling anything.
The sheet is fine. The simulation is artificial by using a standardized squad and formations, but this alone does not mean that it couldn't represent what is happening. AoE is fairly straight forward, there are not THAT many variables in the game outside of the ones that have already been considered by the calculation.
Not to mention, nowhere does he explain the methodology he used in generating such stats. Which equations, which model, which representation. He just puts graphs on a paper, says he did 2500 repetitions and calls it a day. That wouldn't fly in a high school physics journal. I'm not saying he's lying. Of course not, but just putting graphs and giving a short explanation is... in poor taste.
He has given a brief but informative description of the test. The calculation sheet he used is linked, where he also explains how the sheet works. It's not a scientific paper, but I am not sure what you're expecting from a gaming forum. This is some of the best and also pretty well documented calculations that I have seen in any game/community.