Okay, so clearly FS wants people to grind for weapons. So why not just make loop this into gameplay even more? Let us find weapons in missions. Not switch to them; it’s just a “mystery” weapon, wrapped up in a cloth or something. Or maybe a case. It could be instanced, the way scraps of art were in VT2 - and about as common - or it could just be “one person picks it up, everyone gets a weapon”.
At higher difficulties it should give players a reasonable chance to get a decent weapon. After the game, they can be presented to you as spoils or war, or have a little opening animation, whatever.
This does not ruin the system that Fatshark clearly wants, but would help alleviate the pain of waiting months or even a year or more to just get a usable version of a weapon you really like.
If players are getting 2-4 decent shots at a weapon of the appropriate power level every mission, it would improve the odds of getting that one they want with the right stats rolled. Tweak as needed/liked. Also would make treasure hunting have more surprises.