And here in lies the differences between your example and BG3. In BG3, shoving enemies off the cliff is both easy and an expected tactic in many combats.
The other differences are that the enemies you're going up against...are generally hostile creatures against whom you might reasonably be able to win a contested check without it being a particularly remarkable fluke.
What I'm suggesting is that the problem isn't so much the mechanic itself as the AI's failure to account for it in their own positioning. I've found that it's generally not that difficult to avoid having your own characters knocked off cliffs. So turning it into an action? Sure, fine. Reducing the distance? That's fine, too. But if it's too easy or too common, I'm asserting that's simply because the NPCs stand near cliffs too often. (For my part, I don't often use it against bosses, if only because I generally want to loot them afterward, which bottomless pits or lava usually prevent. Nere isn't that hard to kill conventionally, and you'll break at *least* one quest by pushing him into lava.)
(BTW, jfutral and Wormerine, there's a range of views expressed in the thread, but both the original poster and mrfuji3 both seem to me to argue that the availability of a 'one-shot kill' action like pushing someone off a cliff derogates from the D&D combat system which is premised, in mrfuji3's words, on "dealing damage over multiple turns to reduce enemy HP to zero".)
