As I said, you seem to be unable to understand the difference between:
A) "Things that PCs and NPCs know"
and
B) "Things that only the DM/players know"
Your entire argument is based on your inability to differentiate.
I do differentiate. It is you who seem to have an inability to incorporate the rules into the narrative.
The rules are there to be used. It is how you incorporate them into your (and players') narrative that will make them make sense.
And yeah, I do consider that metagaming, because you didn't have the other giants pile on - they've got no idea when he's actually dead. You, the DM, do and used that meta knowledge to cheese it. Which is fine, it's your game, but don't say it's not metagaming.
I still claim it is not metagaming. The monsters will not do it to a fallen character unless proven that it is possible to for a fallen foe to rise up again and fight.
A metagaming perspective would have all foes do this every single times. I repeat. They would do it every single times. The simple fact that I do not do it every time shows you that it is not metagaming. The foes must have a good reason to do this.
Also part of what you described is incredibly odd description:
Damage causes death saves, not attacks. Damage. If he didn't hit and do damage, it doesn't cause death saves, and the player is going to be like "What the hell man?" about your description. Pretending all the death saves were caused by the stomp is pretty weird and helps illustrate how problematic this whole thing is.
Odd? Wasn't it clear enough?
Well, let's go into the mechanic.
Remember that everything happens simultaneously (more or less) as a round is only 6 seconds.
As the DM. I decide before hand how many will attack whom.
3 Giants attack Sir WallofSteel. 1st one hit with a critical and downs Sir Wall.
The second tries to "finish" hits two times but do not kill Sir Wall, only forcing two failed death saves.
The last one misses one attack and succeed the second.
The fourth one goes on with a boulder throw at the rogue and misses.
A pretty boring description don't you think? Compare this to that.
"Sir WallofSteel falls again to a lucky blow from one of the giant. The three remaining giants do not cheer this time. They know that Sir WallofSteel might come back from what should have been a mortal wound. One of them try to strike Sir WallofSteel with it's great sword but misses twice because it is still attacked by Fastfingers (the giant hits but only causes two failed death save). The second crushes Sir WallofSteel's head under its foot to the absolute horror of the group. "Try to get back up from that! Insect!" Yells the giant. The last one, moves in on Fastfingers and throws its last boulder at her but misses. The other three eye Bandaid suspiciously and start to close in on him. Jack the Sorcerer Supreme starts and other invokation of cone of cold..." (quoting myself here...)
This is the mechanic into words. Though the giant did hit, it did not kill the character right away. Describing this as a miss is much better narratively. Having the last giant "stomping" the character to death, adds more drama than a simple sword strike and reminds the players that a giant can and will stomp you. Call it flavour, color, style or whatever. It adds to the game narrative and that is all that is needed.
I case you don't know, all rolls are made in the open. Players know exactly what were the rolls and how it killed/missed/hit/save and whatever. They know. What they want is the narrative that the scene will trigger.
A player saying I hit for 39, 15 and 17 damage is boooooooooring! The rolls are good yes. But I much prefer when a player tells me.
I strike my foe with no consideration to my defense and swing like a madman to bring the giant down. (Tells me how much damage, and I confirm its death). My sword fully connect with the giant's heart as he is bending toward me to strike me down. With a dumbfounded look on its face, the giant falls. I step aside so that the giant does not fall on me. I point the other one and pass a finger accross my throat. "You're next!" and I move towards it.
Here the barb used reckless attack and used the -5 +10 damage option of the GWM. He attacked three times because he got a crittical hit and he is a great weapon master so used his bonus action to attack a third time. A total damage of 71 was quite enough to kill the giant. Yes the attack was made three times, but narratively, one big hit strikes the imagination a lot more. He then uses his movement to go toward the other giant to help his friend.
As I often say:" Do not confound style with ignorance." and "You should always assume that the person in front of you is as knowledgable as you are on the matter."
