MG34's suppression isn't that great either, but IMO it has better accuracy and killing power than other HMGs especially if you give it accuracy bulletin. But a lower ROF. I would imagine it's similar for Vickers
The MG34 suppresses about as fast as the MG42 last I checked... It just had garbage damage. Which makes it a reasonably good HMG. It suppresses blobs in 1 burst, like the MG42. Quality HMG, does its job.
Adding acc should just make it better, as it is unlikely to kill before suppression.
There is a magic suppression per second/damage per second ratio, if its high enough the squad is suppressed before model kill. Some HMGs are tuned right to suppress before end-of-burst cooldown. The MG42 has that tuned really nicely, and that's why its the best HMG in the game. The MG 34 over shoots that ratio, so adding acc (pure +dps) is fine. The Vickers undershoots that ratio and just has low suppression/second so it both kills the model, giving the target squad time to lose some suppression AND gives a big enough window for a second squad to just walk past. The gun can't stop a 2 squad push to save its life, literally.
The Maxim just has low suppression. Get 2 and it works alright vs blobs due to massive AoE suppression.
DHSK and M2 are good, just low field of view. Not good at locking down areas like a large FoV gun like the Vickers SHOULD BE. M2 used to be down right oppressive as it could back up and set up fast enough to suppress the squad flanking it.
This topic comes up like clockwork every couple months and was heavily discussed during the Patch Discussion phase, without any changes (this is the Commander and Egregious Balance Patch, not General Balance Patch). My understanding is fixing the Vickers means it becomes a MG42 clone, which would make UKF even more standardized with OST. Something the balance team is aggressively fighting.