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The problem is the scenarios which are compared. I'll say i do not fully agree with the point you are against it, but the whole derailments makes little sense as well.
Basically the only post making anything reasonable is MMX one.
I agree with some of your initial points about AOE-mortar-blobs but it's such a hard situation to fine tune due to unit volume/saturation.
Let's hypothetically double the radius of mortars while only affecting the far range profile for that extended range. Say the damage is as low as 10. How many mortars do you need to achieve wiping capabilities? This things would only apply to 2v2 or 3v3+ as it's easier to form static frontlines.
I don't agree with Viper that MG + Mortar goes hand in hand because they suppress squads and THEN they do dmg on those squads. MGs + mortar work together because they create frontlines and slow down the pacing of the game. A suppressed squad will more than likely retreat before getting hit unless it can achieve any sort of role for been in that position or another unit can bail them out by taking the MG.
This doesn't mean what Vipper said about MG dps is incorrect nor what he stated about suppression. It's that inconsequential towards what he tried to justify.
Going back to original topic, i think you are confusing design with balance and trying to replicate what IRL does vs what the game tries to achieve.
I think MGs are mostly fine as they are early game but drop the ball late game.
I think mortars are just fine as how they perform but not necessarily the cost effectiveness nor the risks regarding their usage in terms of what they accomplish compared to another infantry squad.