For the record, I think the ability score requirement for multiclass dedications is absolute hogwash and will be never see the light of day at my table.
I suspect that their origin is somewhat tied to the same reason that they arbitrarily limited the feats to second level. I think they feared the Dedication feats were too powerful, so they attempted to mitigate the power by giving them a higher prerequisite.
If the benefits of a dedication feat were tiered, and you only by default got the first tier when you take the feat. You could for instance grant a 'bonus' tier if your relevant stat/stats are high enough, reflecting your aptitude in your new studies. Remaining tiers would be unlocked either via advancing levels or buying additional class feats in the dedication, perhaps. It would also mean that you could have a person dabble in another class even if their stat wouldn't make them a savant in it, it would just slow their progress.
As to retraining a class, it is absolutely a way you could end up resolving it, although playtest had extensive retraining rules allowing you to retrain tons of things, notably excluding class. It makes perfect sense that a potential prerequisite to shifting to another class would be picking up the multi-class in the new class. Then next time they earn a class feat, instead of taking a second multi-class feat in the transition, you could let them switch class, and have them start with 2 multi-class feat in the original class. However, that leaves you at minimum of 4th level, so they jump seems really big. If you could start at 1st level it would make such a transition significantly more believable in my view, opening a potential transition at a lower level.