Then the problem is the content. Relaying on a simple "fix" like grinding and level scaling, gets old quickly. It's not about gameplay anymore, it's about the grind (grindplay), a constant run after the next big thing, because there's nothing good other than that. Again, to me, that's no content, it's just lazy development.
It gets frustrating in SP where it becomes a cheap trick to guide the player through the word, giving the impression of a sandbox type of game, where he can go and do whatever, but in reality he can't. Also the suspension of disbelief goes out the window (tens of bullets in guy's empty face?!; pistol bullet doing more damage than a rifle one, etc.) and it can go even against the story itself ( like the The Witcher 3, if you don't mind mentioning another instance where this gets really bad).
In MP was even worse than War Thunder or World of Thanks. You get a bracket for the levels of players and also the items available to the player on the same level vary wildly, with the difference between base and high end stuff, from what I have, is around 2x or greater (if I remember correctly) and I've met players which have much better gear than me, at the same level, which allows them to kill me just based on DPS - no strategy, to tactics, no nothing, just runs towards you and mops the floor in about 1-2 sec. If this happens to the players on the same levels, what happens to those on the lower end? What happens when a squad of those decides "to have fun"? I've met those too, none could stand in their way.
It's adrenaline pumping when you know a single guy can take out your squad even though you have good gear, but you don't pay attention, when you actually have to plan, when you're vulnerable and the enemy is as well. To have him madly shooting at your face while you light your imaginary cigar, pull out a handgun and one shot kill him... that's no fun, that's trolling and really bad game design. They should instead really start to innovate, both in AI terms, but also advanced gameplay loops, beyond pew-pew-pew... pew.
m2c