If you're talking about Shujinko going through decades, just by entering a pool, then that has nothing to do with entire realm. It is literally just a nonsense they made up with Kotal Kahn being a bodyguard.
This isn't the first time they are contradicting themselves on a spot.
King Jarrod. Killed by Shao Kahn. Killed by Sindel. Killed by D'Vorrah
or Cryomancers.
Deadly Alliance/Deception stated clearly that Cryomancers lived in Outworld and that Frost and Sub Zero descended from them.
MK11 Skarlet tells Sub Zero that he is from Outworld. His bloodline comes from there.
Aaaaand now comes Sindel and says that Cryomancers were Edenians. GG.
So yeah. Nothing surprising that they messed up with Kotal Kahn's background. They simply don't give a shit.
It's not actually the pool, even though yes, this makes a difference on his appearance.
Actually, I was mentioning the fact Raiden encounters a middle aged Shujinko and tells him about the Deadly Alliance. He invites Shujinko to battle them, but the latter has stuff to do, so Raiden leaves to battle Quan Chi and Shang Tsung with Frost, Jax, Cage, etc.
Meanwhile, Hotaru puts Shujinko in prison, where he spends DECADES (referred as "an untold years", but Shujinko then refers to it as "after all these long years", even though it doesn't seemed to be decades judging by Dairou's comment) and he gets out very old. When he reunites the Kamidogu and meets Onaga at the Nexus, that's the end of Deadly Alliance, as Raiden fights the two sorcerers at that exact moment.
So either Deadly Alliance took a long time between Raiden abdicating from Elder God status and reuniting warriors and fighting Tsung and Chi, or time flows differently between the realms. Or, Shujinko keeps getting old because of the pool, that could make sense and explain his sudden aging, however, he did stood imprisoned for "long years"
Still, I think the comics messed up on that matter.
About Jerrod, well, that's obviously a conflict.
About Cryomancers, however, it is stated Sindel banished them from Edenia, and they were natural from there (MK11). My guess is that they settled in Outworld, so if they lived there and had descendants there, they were Outworlders. I mean, Sub-Zero is an Earthrealmer, even though his ancestors are Outworlders, he isn't consider a foreign because he descends from another dimension, and by the same logic, his ancestors are indeed Outworlders, regardless of where the oldest generations were born. Seems conflicting, but can easily be arranged.
Besides, Outworld is basically the union of several other small realms and races, it almost sounds like my country. We have natives, lots of africans, portuguese, dutchs, lots of italians, asians, germans, poles, etc. mixed and in the end we are brazilians. But if we pick up, let's say, an italian, maybe during the time the person got here in the XVI century he came from Firenze, but if we go to the ancestor of this person by 400 A.D., it's very likely to be someone from northern Europe, nowhere near the ethnicity of the italic peninsula, but migration does this.
That's how I see the flow of migration of cryomancers.