Is this mechanic fun? Does it add more to the experience and the gameplay than it takes away? No. Fake difficulty at its worst.
At best, it's an annoying mechanic that lacks a proper, non-RNG method of defeating which guarantees losses over time, and denies player agency over its prevention.
That said I accept your challenge and I will crush this mod at the hardest possible setting despite the RNG nonsense.
Fake difficulty? It's easy to take the control of the situation, it's not a hard game to learn. If there is no RNG-based difficulty, you have a game of chess where everything is dependant on the players (and their in-head RNGs). However this is no chess, this is an actual simulation. Which means, it gives you many, many tools, but balances it out with RNG, ie random events that cannot be guessed at, simulated entropy. Shit, every shot is a random event, unless you can get 100% accuracy.
Player is not be able to prevent losses, sure. Sometimes even when not making any mistakes (or thinking he didn't... which is a far more common occurence). That's
a) Realistic - a war without losses is a dangerous fantasy, not serious Science Fiction.
b) Besides the point - preventing losses is NOT the goal of the game. The goal is to defeat the Mars Governor.
Sure there is no 100% reliable counter to psi. A 100% reliable counter would be boring as hell. You need to use multiple counters, the more the better, and have contingency plans, and neccesary soldier numbers to have reserves. This is not theory, this is what I do. And I never felt like psi is especially dangerous if you're prepared for it, more like - annoying.
If there was no RNG, no unexpected events, what'd be the role of the player? A well-trained rat in the labirynth? A good game should train your braincells in general flexibility and resourcefulness, else it's a pointless activity. A player needs to able to face the game like a human (challenges to overcome with no clear solutions), not be forced to become a trained animal who, after discovering 'way to beat the game', simply goes though the motions repeatedly until wins. At least that should be the target of game design.
Save scumming is something you simply grow out of at some point, when you discover it makes the game boring.