1. For some people game is fun only if it's easy. This might be the case.
2. It's impossible to make every single customer happy. Impossible.
As long as you're not proposing any changes that will make game more fun and at the same time not easier - I'm okay with this.
But for now the only problems you see in game is that you can't stunlock scrakes, you can't instantly kill FP's with 1 demo, etc.
At the same time I didn't find any suggestions about making the game more fun in your first post.
Ah yes well, while there should be some fun for playing the highest level in the game you should also take into account that it is the vast minority of players who do play at that high difficulty. Some balancing around that level is entirely fine but this is not a competitive game, it is a co-op game with multiple difficulties. That said, a lot of people came over from KF1 and really liked how different classes had a lot to offer in that game. This game should have been no different.
However here is some actual problems: Ammo is pretty scarce and while you would think that would incentivize walking around to get ammo boxes the ammo boxes are nowhere near common or give a decent amount of ammo. Perks are nerfed left and right rather than giving each one something good so that it is merely a preference rather than a race to see which ones are viable because so and so perk was nerfed into oblivion.
Ammo - Should be more plentiful either in boxes or in extra ammo for all classes. With the bullet spongeyness of enemies...forcing people to hopefully not run out of ammo automatically favors those who use less ammo or get more out of their ammo. Case in point, Berserker benefits mainly (Martial artist too most likely)
Classes - Everybody should technically be good at some things not homogenized.
Commando - Major trash killer, can kill trash with ammo to spare and is very effective at anything that is not big zeds.
Support - Should be well balanced and effective at most things though not a specialist as they can give ammo to the team and have nice AoE for trash with penetration. Ideally release AA-12 was fine.
Berserker - I was against the nerf to the damage on both the zweihander and smash but honestly besides that nerf the other changes are relatively fine. Tanky, good at taking out trash. Moderately ok at taking out FP due to pulverizer.
Medic - Medic heals. It is good though disappointing they had to nerf armor healing. Mediocre at taking out big zeds, gets by killing small zeds, heals the entire team. So all good.
Firebug - I'd like to say this perk should specialize in killing scrakes in this game because they are effective at that but to be honest they are effective at everything. So jack of all trades it is (Support should be brought up to firebug level)
Demo - Needs massive buffs in order to do his job and actually be a specialist in everything big zed related. He may not have an excess of ammo for his most damaging weapons but others should be available for him to use much like in KF1. Right now all the weapons are too expensive and it takes forever just to get anything decent as refills for ammo are per shot and are not cheap. Basically, Kill FP and Boss mostly with slightly less effectiveness for scrakes.
Gunslinger - This should not be all that effective vs big zeds and represent the trash killing half of the old Sharpshooter perk. The many different guns should reflect that.
SPECULATION:
Martial Artist - Big Zed killer specialist for melee.
Swat - Tanky specialist that is well rounded for guns.
Sharpshooter - Big zed killer for guns.