Losing the loot does seem like a good penalty to balance the power of this mechanic, similar to how Disintegrate (Black Blade of Disaster etc) worked in Baldur's Gate 2.
In most situations there's no loot to loose except a crappy weapon or item. And even with some bosses like the Matriarch, you just don't loose anything.
It does not really "balance" anything and it is not a high level spell you'll use wisely : it is a common bonus action.
Just look at the screenshot above for distance. Not sure anyone would consider that the entire red area as being "near the edges of cliffs"... Especially if you consider in game units of measurement.
For trash encounters, you don't necessarily need to throw enemies off cliffs to win. You can simply shorten the duration of the fight, save some resources, and still have fun. However, if you do push Minthara off, you would indeed miss out on a significant loot. It's a trade-off that players need to consider when deciding whether to utilize the shove mechanic in such situations.
As for the distance, I can agree that it could be adjusted, perhaps decreased. However, it is important that the shove mechanic reflects factors such as the strength of your character and the weight of the enemy, which I believe are already taken into consideration.
