If you rewritten the story...

[Commander]

I doubt Raiden or any of the Earthrealm warriors could do much to save Sub Zero given the fact that they were in the middle of a colosseum with thousands of spectators watching, almost all of Shao Kahn's minions being present or ready to on call, a whole bunch of the Lin Kuei, Sektor, Cyrax and most importantly Shao Kahn himself being present, there was really nothing much they could have done.

Raiden could have EASILY saved Sub-Zero the same way that he saved Smoke in the Living Forest against 4 robots, Shang Tsung, Reptile and Kano.
Afterwards, he could have teleported himself and the other 4 the same way that he teleported himself, Liu Kang's corpse, Johnny Cage and Sony Blade after he defeated Shao Kahn.
There's always an explanation and a possible solution for it.
The fact that ED Boon did it anyways because "a character that wasn't cyborg may be cyborg this time around," is another story.

As for Shao Kahn's minions, the only people I remember being in the arena were Kintaro, Ermac, Shang Tsung, Quan Chi and Reptile.
Kitana had left the arena because Kahn had been mad at her for allowing Cyrax and Sektor into the arena.
Scoprion is neutral.
Raiden, Kung Lao, Liu Kang, Johnny Cage, Smoke and Sub-Zero were also in Kahn's Coliseum and I don't see how they couldn't have evened up the fight.

Plus, what does spectators have to do with it?

 

[Flying Jinko]

Raiden could have EASILY saved Sub-Zero the same way that he saved Smoke in the Living Forest against 4 robots, Shang Tsung, Reptile and Kano.
Afterwards, he could have teleported himself and the other 4 the same way that he teleported himself, Liu Kang's corpse, Johnny Cage and Sony Blade after he defeated Shao Kahn.
There's always an explanation and a possible solution for it.
The fact that ED Boon did it anyways because "a character that wasn't cyborg may be cyborg this time around," is another story.

As for Shao Kahn's minions, the only people I remember being in the arena were Kintaro, Ermac, Shang Tsung, Quan Chi and Reptile.
Kitana had left the arena because Kahn had been mad at her for allowing Cyrax and Sektor into the arena.
Scoprion is neutral.
Raiden, Kung Lao, Liu Kang, Johnny Cage, Smoke and Sub-Zero were also in Kahn's Coliseum and I don't see how they couldn't have evened up the fight.

Plus, what does spectators have to do with it?

Outworld is Kahn's realm and trying to pull off something like that when a tournament is going on would never work well in Earthrealm's favor, given the fact that as of that point the only thing keeping Earthrealm safe is their abiding of the tournament rules and not starting any unwanted altercations with Kahn, which he would use as an excuse for invading Earthrealm. Also remember besides those who were present there is still has his lesser minions and other guards of call (like the beast we see tied up close to the arena. They could have saved Sub Zero, yes, but they would have put themselves and Earthrealm in jeopardy.

 

[Commander]

Outworld is Kahn's realm and trying to pull off something like that when a tournament is going on would never work well in Earthrealm's favor, given the fact that as of that point the only thing keeping Earthrealm safe is their abiding of the tournament rules and not starting any unwanted altercations with Kahn, which he would use as an excuse for invading Earthrealm. Also remember besides those who were present there is still has his lesser minions and other guards of call (like the beast we see tied up close to the arena. They could have saved Sub Zero, yes, but they would have put themselves and Earthrealm in jeopardy.

It would work, because MK9 has taught us that the Elder Gods don't give a crap about Mortal Kombat tournament rules being BENT, as long as the rules aren't BROKEN and invasion doesn't take place.
Raiden even argued this with the Elder Gods, and they did NOTHING until Kahn invaded Earth and almost beat the living daylight out of Raiden.
Raiden could easily argue with the Elder Gods that saving human Sub-Zero was important to deciding the fate of EarthRealm since he is an EarthRealm warrior.

As for the lesser minions, all of the Mortal Kombat heroes fought off those same waves of Kahn minions and Lin Kuei robots, right before Sindel came in the story and killed most of the good MK warriors off.
Not to mention that LOTS of the fights in story mode consisted of 1 vs TAG matches anyways against other MK warriors, so killing a few guards and minions should be no problem for them, especially with the God Of Thunder on their side who single-handedly shocked and destroyed the Lin Kuei robots with 1 electric shock in the Living Forest.

As for the tied up beast, if he's tied up he can't get loose anyways, and the good MK warriors could all ambush Kahn and kill him before he tried to release him.

 

[Kotal Kahn]

Since we don't know how powerful the elder gods truly are, I would've given them a larger role.