A lot of alternate methods of granting advantage have far greater costs/downsides for using them (and might only work for the attacker only, not the whole party + they're class specific while EVERYONE has shove) compared to a theoretical bonus action shove to prone, and shove being a bonus action is likely the exact reason why we don't have shove to prone implemented to begin with. It basically rounds back to one of the major arguments in regards to height advantage/disadvantage last year, in that its existence meant that the value of advantage-granting spells like Faerie Fire were diminished greatly for ranged characters.
There's massive difference between height/backstab advantage and advantage after shoving prone. The former has no real action economy cost and 100% reliability without investment, the latter costs 1 attack (or ba*) and reliability ranging from 40% to 60%. It's not even close in terms of effectiveness.
Everyone has shove, but not everyone has shove that is remotely worth using unless it results in one shot of an enemy with significant HP. Since you are targeting the better of Dex (Acrobatics) or Str (Athletics) it's almost never useful for a non-strength character without athletics proficiency.
*Most other things you wrote is based on assumptions about how Larian will or will not implement things. It's everyone's guess. If we however assume that bonus action shove prone is added, it doesn't cause any major imbalance between combat roles. DnD 5e is already skewed towards spellcasters and ranged. Giving a little and still questionable boost to melee is not a balancing issue.
So let's stop pretending that the biggest issue of bonus action shove for most people (however endowed with 5e expertise they might be) isn't the one shot potential.
It's not just about advantage for 1 person for one hit.
I did not imply that is not. Circumstantial usefulness beside DPR increase of prone shove matters slightly, but BG3 already offers you alternatives. It's not like without shove prone you can't react accordingly to any situations you mentioned.
@Maximus
In play I barely find an occasion to use BA shove. Jumping and use objects occupies a lot of my BA uses for most of melee characters even if they don't have any class BAs. But maybe it's not true for how other people play.
My point was not that shove isn't problematic. However I don't believe that changing shove from bonus to attack action helps if AI remains smart. AI should use shove to replace attacks if it has a chance to one shot a player character. Furthermore currently the enemy can't jump to high ground and shove your archer down, but if Shove was tied to just Attack it could.
Making range shorter helps, but I think that there is one other thing to consider - shoving uses contest rolls (which are core 5e rules). Contest rolls and DC 10 (which is Larian is pronanly using) makes defenses against shove just not reliable. 8 Str goblin with no athletics proficiency has 23% chance to shove 18 Str Lae'zel. If shoving was changed to use rules similar to that of the spell (base 8 DC+Dex/Str modifier+proficiency[acrobatics/athletics]) the chance drops to 5%. You can see the differences in expected success of shove attempt between contested/DC8 and DC10 here:
![[Linked Image from i.ibb.co]](https://i.ibb.co/T4Hy6gy/Contest-DC-8-and-DC-10.png)
y axis - success chance
x axis - difference between attackers and defenders modifiers
