It isn't at all. Bernoulli never asserted that particles are bound in any way, he just discovered a relationship between static and dynamic pressure. I don't know why people apply his name to the equal transit time theory of lift; there is no real association.
Perhaps because it is always drawn that way, that the same streamline gets separated then goes over the wing, then goes back together. Then in big letters it says Bernoulli principle.
Now that I read about it more, it looks like Bernoulli's principle is just conservation of energy - and as you say, there are no other requirements.
If you don't assume equal transit, then there's no reason to expect the particles above the wing to move faster than those below. And without that, there's no reason Bernoulli's principle would come into play at all.
There are other ways to expect differences in velocity. A bit like the venturi effect in a pipe constriction, a constant flow rate will have to involve faster velocity when the area of flow reduces.
If you trace a line on the wing cross section between the stagnation point and the trailing edge you will see the upper surface restricts/squeezes the flow more than the lower surface. So with a constant flow rate, the upper velocity will be higher even without equal transit.
Yes there is. Suction on upper surface to maintain attached flow -> lower pressure -> increased speed to conserve momentum. Bernoulli's relationship holds true along a streamline, equal transit time doesn't.
