Hussar
Legend
Why isn't it fine to have a story in which malaria can be shouted away? I might read that story. It sounds intriguing.
Trees are real. No treents? Lizards are real and never talk. No talking lizards? I've never found a fantasy world in the back of my closet. No Narnia?
Besides, everything has components of reality in it somehow. We know how making hand gestures and speaking works, for instance. Those things should be treated somewhat realistically, your argument suggests. So how do those things produce a phantom horse? Seems like wizards are failing to treat them realistically in D&D. Your principle needs a second principle to determine its application.
But anyway, you seem to be trying to impose a principle here that would serve to put constraints on where our imaginations can take us. Why? What does this principle give us in exchange for constraining the kinds of stories we can tell? I'm not sold on its value, and just asserting it will not convince me. D&D is fantasy, and its unsupported departures from reality are part of its charm.
This is an argument that is as old as D&D. One camp seems to plunk itself in the "Myths and Legends" realm where supernatural occurrences can be performed by anyone. The other camp sets itself on the hill that says that anything that cannot be done in the real world must be done by magic. That a fighter, because it doesn't have spells, must be limited to real world physics.
And, frankly, these two impulses are probably the root of so much of the friction between fans that I really don't see any reconciliation.