I think that, even with the Key magic being properly explained, it is still too hard a pill to swallow.
CLANNAD has lights that can grant any wish, in a world where everything else is normal? And you can gain multiple lights over alternate realites??? If that isn’t stretching it, then I don’t know what is
And Little Busters has people unconsciously creating a dream world that spans multiple days and repeats as much as they need? That’s just crazy talk
I think the problem with those cases of Key Magic is that there is just no sort of explanation to the mechanism. If, for example in clannad, they put in stuff like “An ancient civilization created these magical wish-granting lights. But these magical lights have been spread across multiple dimensions” then sure, I can believe it. But all that would do would be to ruin a perfectly good story.
Which is why I don’t bother understanding nor justifying the Key Magic. I just focus on the emotions