No physical model is objectively true, especially not on the macro scale and doubly especially not with regards to fluid dynamics. A physical model is only good if it is a reliable predictor of events in the real world.

When racing, I spend a lot of time worrying about the shape of the slot and the airflow through it. The folks placing first in regattas seem to have the same preoccupation. I'm also trying to get the mast prebend thing down to prevent the mast from from bending into the slot and close it off. Sometimes in heavy air I close off the slot to invert the main and power down.

So, much of my thinking about sail shape is influenced by my personal theory of the "slot effect". It may be that the effect of my actions is better explained by some other theory, but that doesn't in itself invalidate my personal theory. Unless I find that I must contradict my theory in order to increase boatspeed, or I come across a much simpler theory, I'll stick with the one I have, thanks.

It's like arguing about whether the earth revolves around the sun, or whether the sun revolves around the earth - The important thing is not which is more correct (accurate models exist for both viewpoint), it's which model is simpler, and the sun-centric model is simpler by far.

Arguing whether a sailboat is sucked forward or blown forward is even more ridiculous - There's a pressure differential and the boat moves to relieve that differential. Suck and blow are the same thing in this context.