I'm gonna quickly bring up the past and appreciate the fact that NRS made Johnny and Kuai Liang have a maybe friendship with each other.
Even though Kuai is hostile towards Johnny, he still entertains him a bit. Compare that to his intros with Sonya where he eludes to intending on killing her.
In mkx he gives the kombat kids a test, specifically requested by Johnny. The fact that he not only has contact with Johnny, but agreed to it says a lot in my opinion. Of course, the kombat kids don't know this, but there's something Cassie says that caught my attention.
"My father always spoke highly of you, Sub-Zero. He wants to talk." - Cassie
"Talking. Always his first choice." - Kuai Liang
How close were Johnny and Kuai Liang before mk1? Besides being mentoring the kids and making sure they become great warriors, (edit) what else? Edit: There had to be more to it. Cassie says Johnny always spoke highly, which means whenever Johnny was telling Cassie about the events that came before, Johnny only had good things to say about Kuai Liang. Kuai in return, not so nice things, but in comparison to what everyone else has to say about Johnny, it was pretty tame. It just raises the question: How often did they talk? I theorise that Kuai could see himself in Johnny to some extent. Johnny remained to serve Earthrealm and is incredibly loyal to Earthrealm (especially Raiden), but was also all too happy to train his own daughter and many others (no shade). Kuai can relate with starting fresh and leading a new generation. Jax left the military, but Johnny stayed even though there was nothing in it for him to.
Kuai had Frost as his student, and I like to think they both have a strained father-daughter relationship. While Johnny doesn't have a strained relationship with his daughter, you can see that Cassie is some kind of identity crisis, having Johnny and Sonya's traits and having to deal with constant comparisons from anyone that knows them. In other words, they've both experienced parent-hood, with the child being reflections of the parent. Frost broke the mirror, but Cassie keeps it intact.
Also, both of them joined the tournament for selfish reasons. Johnny for his career, Kuai to avenge his brother. You could argue that it's the same for Sonya and Jax, but they were actively working for the military, while Kuai went against the Lin Kuei.
Now I'll show one of his mkx intros:
"Do you not recognise me?" - Kuai Liang
"How'd you get un-cyberised?" - Johnny
"The one benefit of Quan Chi's process." - Kuai Liang
Here's what I find funny. Why would he need to question Johnny about this, considering they've barely had an interaction in the mk9 storymode. (The rest of the intros are comically bad, so I won't transcribe them)
All of the intros Johnny has with Kaui Liang in mk11 are pretty chill.
Now compare those with this one.
"A good general is hard to find." - Kuai Liang
"What's that supposed to mean?" - Sonya
"Your soldiers are going to miss you." - Kuai Liang
What he mean by that?
"There's only one leader here." - Sonya
"Then prove yourself worthy." - Kuai Liang
"I proved that a long time ago." - Sonya
Kuai Liang (supposedly) respects Sonya more than he respects Johnny, and yet he says things like this to her??? Shows the potential closeness Kuai Liang had with Johnny in the old timeline. Kuai Linag and Hanzo friendship is great, but we were robbed of the idea of Johnny and Kuai Liang.