College players can keep developing against older players and there is no salary. Disadvantage is they can stay in college and eventually walk to free agency, though it happens very rarely despite our PTSD about Petersen. Johnson would be giving up a lot of money and an opportunity to get to RFA/UFA in the NHL earlier by not signing.
Money, at least in the short term, yes. As far as RFA eligibility goes, there wouldn't be any difference as to when he'd be eligible if he signed with the Sabres at the end of next season, or didn't sign with anyone until the off-season. A player has to have a certain number of professional seasons to be RFA eligible, and the number of games an NCAA player can get by signing after his season is over isn't enough to count. Actually, even signing this off-season would not make him RFA eligible any earlier than he will be next year, due to his age.
To digress, here are Johnson's ELC and RFA situations based on when he signs his contract:
2022 offseason: 3 year ELC, becoming an RFA in 2025.
At the end of the 2022-23 season, with his playing in the NHL: 2 year ELC, ending in 2024, then a year of pre-RFA eligibility (Mittelstadt had this, and accepted his QO that year), then a full-fledged RFA in 2025
2023 offseason: 2 year ELC, becoming an RFA in 2025.
So, pretty much unless he has a huge rookie season in 23-24, under scenario 2, so that the Sabres want to sign him to a big extension right away, his RFA outlook is pretty much set regardless of what he does.
As far as UFA eligibility, he'll be UFA eligible in 2029 regardless of anything. That was set when he returned to college for the previous season.
Things get overlooked. I'm not surprised that things like this happened and it started at some point, I'm surprised it hasn't been dealt with somehow before now.
I hope this is something that teams really push to get solved whenever the CBA gets revisited, if not before. Teams and their fans deserve better. If there are individual cases where a player feels a team is being vindictive and actively trying to block their development or doing something harmful to the player's career prospects, there shoudl be an aribitration mechanism to resolve those rare cases.
It has not been "dealt with" because it is not a loophole. It is a deliberate decision in the drafting of the CBA.