Do we actually know how this free tuition situation works at this point? Someone can correct me if we have other information but my best guess would still be that Burke is using his power to cook the books and simply mark the tuition as paid. What portion of the money from Quinn's restaurant goes to him or how many free samples he gets I don't know, but I would be surprised if Quinn was paying girls tuition upfront each semester.
We know almost nothing about the details of the free tuition. We know it's rumored, and we know Quinn has tacitly promised it to Maya and Mona (and presumably Camila). That's about all we can say for sure.
If only the MC had asked about it when Sage was explaining how sororities are supposed to work. (I'm not complaining that he didn't, but it could have answered so many questions!)
At the risk of triggering a deluge of examples you feel prove otherwise the vast majority of gaming systems are arbitrary. The characters, production value and writing (in spots) may be enough to trigger a lot of interest and debate but it is still a game that requires such a system and not a novel. Remove the system and you basically get only a visual novel with even less choice.
All game systems are abstractions, and they invariably have flaws. But there is a difference between a flawed abstraction and an arbitrary one. A flawed system has a relatively clear set of rules that govern it, even if sometimes the outcomes don't match the rules. An arbitrary system has either no rules, or has a very complex set of rules with lots of exceptions.
The affinity system is already hamstrung by having to conflate sexual immorality, aggressive violence and drug use. But even then, the clearest rules for what constitutes a Major Choice I can come up with is something like the following: decisions that can lead to soliciting prostitution, starting an affair with someone in a romantic relationship [except with a main LI], the chance to run away from a fight when possible [possible being somewhat vague], the decision to turn down non-alcohol drugs forever.
That's not exactly a smooth set of rules, and it still leaves out the decision to forgive Steve. I'm just chalking that up as a one-time flaw, because there are so many counterexamples of the MC holding a grudge (repeatedly saying he hates the Jocks, hard feelings against Quinn, hiding behind Karen Rebecca Johnson instead of talking to Maya) or giving people second chances (trying to defend Chad, no hard feelings against Quinn, forgiving Maya/Josy/Jill/Maya again).
So yeah, in my opinion the easiest way to define why something is a major choice is that DPC said it was. That's fine, this is his game. But it it makes the system feel like a game mechanic more than an attempt to really flesh out who the MC is. That, to me, is arbitrary.