So, as it is, experimental weapons are cool, but too much of a power hike too soon.
For example, in my current game, I found an experimental Kpist just before leaving Norra Saltholmen for the mainland. Sure, now I have a kickass gun, but I will also no longer have the excitement of finding a better quality Kpist in this playthrough, because there are none.
One solution would be to push the Experimental drops much further (later) in the game still, but this would needlessly reduce interesting content from the early game.
So, my suggested solution is this: Instead of experimentals just being the last tier of a given weapon, make them into their own separate weapons, subject to the same quality tiers as the standard ones. This way, finding one would still be exciting without making future drops of the same weapon completely obsolete.
For example - and I’m gonna use some made-up numbers here just for extra clarity:
I have a Worn quality standard Kpist. It has an effective range of 70m and a spread of 1,5. It does its job.
Then, I find a Worn quality Experimental Kpist. It has the same values, but also an added Overdrive mode.* Woo, upgrade! Happy days!
I later come across a Good quality standard Kpist. It has a higher effective range of 85 meters and a smaller spread of 1,2. Now I get to make an interesting choice; Do I want the better general performance at the cost of losing the Overdrive mode? I decide to keep both because hey why not.
Later I find an Exceptional quality Experimental Kpist, which is an upgrade over both having 100m range and 1,0 spread PLUS Overdrive, spinning the cycle of upgrades another rotation further. And on it goes.
(*: This example assumes that currently the experimentals are identical to the yellow Special tier, but with the added special property. If they are not, adjust accordingly.)
I don’t know how hard this would be to implement, but it would smoothen the progression/power curve, while keeping experimental weapons interesting and still allowing them to drop early on so as to not make early game too dry.