I don't really get why people want a leveling up system. It's just filling bars and it just forces people to unlock things
in order. I like the current system much better. Plus, on the flip side, if they were to listen to the feedback about a leveling system in order for that system to even work they'd have to entirely rehaul how unlocking works
period. Mods for everything would have to become level locked, guns, boosters, and so on would have to become level locked...
And then there's the fact that Uncharted Points and Relics can completely negate/bypass those level restrictions. And while you can already technically do that, it's not the same thing because... there's no levels. People can choose to focus on something to unlock what they want. Yeah, it means you need to do a ton of work to get everything as opposed to a standard leveling system but even then a leveling system in and of itself is a
grind.
Anyway, chances are they aren't going to go back to a leveling up system. That's too much work for so, so little gain. And it's not even really a feature, it's just a thing people are used to having because it was like that in UC2 and UC3 MP (and other multiplayers, of course).
And this doesn't even touch on how skins wouldn't be tied to leveling up like in the old games. That whole leveling up system in the previous games was as much about getting/unlocking weapons, mods, boosters, etc as it was about getting cosmetics. You had a
drive to unlock character skins. Without those, it really just makes more sense to have the current system. Otherwise, waiting until level 35 (just an example level) to use a decidedly shitty shotgun wouldn't feel very rewarding.