There have been posts regarding this issue before, as far back as early 2021 and the most recent being December 2023.
DF needs to fix this. Italicised below is a quote from one of these previous posts since it basically describes the problem.
“If I want to upgrade my gun, I need to find some obscure squad number 3781 that I never intended to use, and then grind it to unlock upgrades. This is just unnecessary and annoying to use.”
I also refer to the similar issue with tanks where certain squads are unable to use certain tanks forcing you to go from your high level squad back to like a level 1.
My suggested solution to this problem is that using a weapon gains XP, and that can be put towards upgrading said weapon.
Now the important point in my opinion would be that once any of that weapon is upgraded, all can be.
So if Ive used the Lee Enfield in one squad a lot, grinded it up to say 3 stars, then all my other Lee Enfields and future purchases have the ability to be fully upgraded.
I would agree its fair to make the player pay silver for each individual weapon to be upgraded, similar to the existing process.
The key difference here is not having to find a random level 1 squad that is useless and grind that just to make a rifle better or unlock a pistol for anti tank gunner or whatever.
One of the previous posts suggested having the stars as a part of the research tree so you can research upgrades or just skip them. Im open to debate whether my option or this other option would be best.
A final note Id like to add is what supposed benefit DF gets from the current system. All it does is annoy players and deny them proper upgraded weapons. Youve also got cases where some squads have heaps of unused upgrade tokens while others have none.
Whether players have to grind an obscure squad to upgrade a rifle or not doesnt give DF any more money. Indeed one could argue DF loses money by this stupid system as it is one of many issues this game has that just turns people off.