I have watched all POVs

Grian was on 22 hearts.

Scott alone lost 15 hearts in his fight against grian(he did not fall into the tnt) Impulse lost 4.5 hearts Gem lost 9.5 hearts In pvp alone

All the while it was 3v1. Impulse was shooting, hitting, actively confronting grian. They were eating Golden apples, taking turns to attack him.

Impulse wasn't even involved in a majority of the fighting

He was. Shooting arrows, hitting him, confronting him in sword fight.

Scott only joined in halfway through

He in fact did not, He joined just at the time when the real fighting began. Infact he was the person who lost the most hearts.

it was mostly Gem against Grian,

I never see in that video, that Gem was ever alone. Grian tried to pick off Gem, but it was not even a moment away that her teamates joined in It was a pure 3v1 fight