I don't see any reason to believe Nix is even considering coming here. But if you're going to compare the two you need to weight their most recent production. For instance, Sims first four games will always have those 8 INTs, but as he gets more experience those first 3 games will be less indicative of his current level of play
So while it is accurate to say Sims has 20 INTs in 17 games (and I believe it is just 17), it's also accurate to say he's thrown just 12 in his last 14. It's also accurate to say he three 7 INTs in effectively 6 games last year.
Last year Nix was a 61% accuracy passer on 323 attempts at 7.1 ypa and 11Tds to 3 INTs in 10 games. As a runner he was a 2.9 ypc with 4 TDs.
Last year Sims was a 60% accuracy passer on 188 attempts at 7.8 ypa and 12 TDs to 7 INTs in, effectively, 6 games. As a runner he was 5.3 ypc with 4 TDs.
Keep in mind when looking at those stats that Nix's includes games against Akron and Alabama State of a combined 29/39 with 5 TDs and 0 INTs. Sims didn't have the advantage of playing against Kennesaw state to help pad stats. Without those two games his numbers look as the following.
59.2% passing on 6.7 ypa with 6 TDs and 3 INts.
Of course Nix also had to play against several while Sims was hurt for Clemson/ND/UGA. Now against Pitt, the best team Sims did play against, he went 24-34 for 359 yards, and 2 TDs, but also 2 INTs. Now obviously he wouldn't have had those same stats against ND/UGA but it's worth noting.
The last thing is the surrounding situation as IMO, Nix was in a better position to succeed and if he came here next year he'd be going from a better situation to a worse situation while Sims would be going from a worse situation to a, hopefully, better situation, so you would expect Sims to be able to improve on his numbers more readily than Nix to improve on his. Especially since Nix already had a year more experience.
In general, I think people need to realize that we're not going to get an obvious upgrade at QB in the portal, and that's not really a problem. With Sims being a soph sitting at 60% on 7.8 ypa and his running ability is not a bad spot for a QB. We need to improve on the OL and WR far more than QB, with the note that we need Sims to stay healthy next year.