May I suggest instead of doing all that extra manual work, that instead you require all fighters to fight every 60 days or so lest they be automatically retired.
That way, all fighters, even "sparring partners" (which I don't see the problem with since they take up to 4/4 or 4/10 spots on your roster) have an incentive to train other attributes, to stay active in fighting, etc.
Further, they would be taken out of their "sparring partner" role in preparation for and after recovering from fights. And if not, they amass losing records or are retired from the game, and their manager's record and hype are dinged accordingly.
I think it's the perfect solution.
Also, people who are just experimenting aren't falsely accused or falsely punished for doing so. There is room for Rickson Gracies and Mark Colemans in this game, imo.