Flanking was a good way to deal with this problem before the slowdown PR (and frankly still is, if anyone dare use it).
I think an alternative should be considered, revert the PR so theres no slowdown, and have projectiles go over crates, and unlocked lockers be able to be opened with 4-5 shots from any gun, and the locker is forced open for a bit (similar to stamina (yes basically adding the stamina system for lockers, don't @ me)). If you manage to pull a locked locker you should be able to get away with it since those arent very easily found in places like maint, where most often (if at all) locker pulling takes place.
EDIT:
Also people push lockers a lot more now, and it looks so janky because pushing stuff isn't smooth. It feels so immersion breaking sometimes.