Two most common things I see in Borderlands Ruin:

Weapon Toss, optional tank ability: Range of 15 yards with a 10 Yard pull-in.
Holmgang: Range of 10 yards that ignores bind and knockback resistance on the target (as per the tooltip description). I'd be very interested to see tests as to whether or not Fetter Ward is a viable defense, I cannot claim first hand knowledge.

Additionally, I have no idea if Z levels are even supposed to be considered fair game or not, especially when you consider how certain classes can practically shortcut down long heights. But one thing is clear: There is no safe zone going up the ramp barring the most pixel perfect position thanks to the cliff overlook, and only one class type even has a counter to the use of such abilities, which may be invalidated in the case of Holmgang. Small wonder you mostly see Warriors pulling these stunts if so.

You also generally have no way of seeing the people doing these things going up unless the radar decides to be generous. So people are at best guessing if they'll be next, which needless to say; depreciates from the overall quality of the match, but does give the team doing it a small tactical advantage.

So for whatever validity there is to knockback as a tactic, there is no denying it becomes ridiculous on Borderlands in particular, this is mechanically allowed just not fun when abused constantly.