So I'm looking for a fighting game, has a lot of singleplayer content preferably, which one should I choose? I already own Tekken 7, not really into NRS games, loved Guilty Gear back when I was in high school but there are so many damn versions on Steam I can't figure out which one to buy. Soulcalibur VI looks pretty sweet, Killer Instict is dirt cheap, never been a fan of King of Fighters so KoF 14 is probably a pass for me.
Your safest bet would be to to get Soul Calibur VI as far as single-player content goes. There are two separate story modes: One for your own created character that has you trotting around the world, and meeting characters, and a bit of C&C; while the other follows the story of the main cast individually (as well as a "main" story so to speak), and diligently maps out the timeline of when X character was doing what. The only issue with the former is that some of the RNG and mechanics don't seem properly balanced on higher levels, and it can be hard to get a weapon with your character's current level. Other than that, you'll probably spend a decent chunk of time in Create-A-Soul mode.
The next best thing would be the NRS games, but you already said you don't like those.
If you're thinking about GG then the latest version is Revelator 2, and that's essentially what you'll want to go get. It has a story mode (It is literally just a movie tho, you never play any fights in it) as well as various character specific challenges/trials, and general ones involving the different mechanics in the game. Do let me pre-face this by saying that if you want to experience the entirety of the story, you'll also have to get Sign (Or you can just YT it). The story in that game is different, and Revelator picks up where Sign ends. If it helps, this is the most technical fighting game next to KoFXIV (which is already a step down in some ways from XIII) of the ones you've mentioned. So regardless, it's a good time.
Dragon Ball Fighter Z is fun, and has a 3 pretty lengthy campaigns, but you'll have to
really like the gameplay. Other than that, it has your typical arcade mode, and the character trials.
I feel like I
should mention that Street Fighter V has a gotten a decent amount of content over the years. A story mode, dozens of character trials, a survival mode (that isn't completely terrible anymore), and a pretty big roster. But, obviously, this is contingent on your enjoyment of the mechanics. As a big SF fan, I was hugely disappointed with the game, but this is also coming from somebody that had to put up with so much shit before it finally got to where it is. It does have its fanbase tho, so you might like it.
Can't speak on KI as I don't own it.