This is just the basics of a system trying to mix more skin customization, reduce the rng for the skin/perks and trying to compensate the actual loadouts you have for each merc.
What about divide the actual loadout cards in 2 parts: Merc+skins and weapon+perks (+skins)
The skins could be dedicated to each merc, so you can still trade up skins for better ones (but only skins), and keep your 383 sparks perks/weapons, but unlock a new shiny skin for that merc (and if you have various mercs with cobalt skins, you’ll still have that skin for that mercs). With this you keep the skin rarity of the mercs and this wont kill all of your cobalts/gold loadouts you actually have.
The weapons+perks will be unlocked too for each merc, for example, if you have a 383 loadout and gold, cobalt, CW, Humble bundle and bronce skins, you can use the 383 set on each skin. With this you reduce the grinding for having a desired loadout with a rarer skin, but you still need to unlock it somehow. Also it could be an option to use the merc skins and apply a different skin to the weapons (so you can have a cobalt skinned sparks with a golden empire in a 383 loadout)
An example with 2 mercs and various actual cards for each one.
Merc: Sparks
Currently cards: 343 (Cobalt Shard), 383 (Gold Crown), 382 (Gold Bamboo and Lead Dirt), 373 (Bronze Woodland and CW), Basic (Basic Skin)
Merc: Proxy
Currently cards: H11 (Bronze Woodland and Iron Galvanized), Ke12 (Cobalt Fragment, Silver Urban and ReV), R22 (Lead Dirt and Gold Swiss), Basic (Basic Skin)
With the system mentioned, the cards’re divided:
Merc: Sparks
Skins: Cobalt (Shard), Gold (Crown), Gold (Bamboo), Bronce (Woodland), Lead (Dirt), CW, Basic Skin
Loadouts: 383, 343, 382, 373
Merc: Proxy
Skins: Cobalt (Fragment), Gold (Swiss), Silver (Urban), Bronze (Woodland), Iron (Galvanized), Lead (Dirt), ReV, Basic Skin
Loadouts: H11, Ke12, R22
And with the divided loadouts you can mix the skins and loadouts, but only for the merc you have unlocked (so if you want the shard cobalt on proxy, you still need to trade up the skins for that merc)
(i hope this is understandable lol)