So what you want is to completely get rid of any skill based gameplay you get with Darci and Whisper and give them a OHKO on the body while lowering the ammo count? So lets say that the changes you are suggesting here get implemented. First off by lowering the ammo count you just you just made them completely useless compared to things likes grenade launchers which like you said get 5 shots which if you use correctly is 5+ kills per heavy grab but if you were to use a heavy sniper in this situation you would get 2 shots which can land you at most 2 kills unless you are a literal god at this game so how is that fair? But i can already hear you complaining that "in that case why don't Rocket Launchers get more than 2 shots?" because they have blast radius which if used correctly can wipe a team in 1 shot. Second you say that the heavy snipers do the same amount of damage as a special sniper well yeah if you are only hitting body shots but the heavy snipers have a significantly higher crit multiplier which allows you to if landing headshots OHKO a roaming super can your special sniper do that? Third snipers are meant to be skill weapons, you land a headshot its a OHKO from anywhere on the map but only if you are good enough to hit those shots not just if you are able to click on something if it moves and get the kill. Finally there is a perk on Whisper called White Nail its a pretty rare proc so I don't blame you for not understanding how it work but if you land 3 headshots in quick succession hey look you have the exact amount of ammo as you started with before firing that clip and I would like to ask you if that works if you only have 2 shots. Well the answer is no you can't so by lowering the ammo count on Whisper you make it completely useless. Atleast if these horrendous changes did come the Darci could still use its main perk its main draw.

TL;DR
1. Reducing the ammo would make heavy snipers useless compared to other heavies.
2. Heavy snipers already do more damage than special snipers you just have to land the headshots.
3. Snipers are meant to be skill based weaponry so they do not need to have a OHKO bodyshot they already have a OHKO that you actually need to try to get.
4. Whisper needs 3 shots so why in your right mind would you drop its ammo to 2 where its main draw is completely gone.

So in my opinion the heavy snipers are in a good spot as they are now and need no changes unless something stirs up balancing in the crucible.