Ouch. Very plausible, and an interesting angle to take. Tidus' relationship to her before was her guardian and hero, and now she doesn't need one, so... er... he's a little extraneous. All the little scenes showing this are so effective. I like the detail that Tidus notices her hiding in the waterfall on slippery footing.
Tiny nitpick: Gippal in the game was very adamant that Yuna was no longer High Summoner and that people should stop taking advantage of her and running to her with their problems. He hired her because she said that's what she wanted to do. "Okay, fine, knock yourself out." He had the Al Bhed irritation with exploiting Summoners, apparently. It's a minor point... a slight readjustment there could reenforce the point you're making, that Yuna's digging because she enjoys the work and getting paid for it, instead of just being expected to sacrifice for others' sake. :) The nail-in-the-coffin on blitzball is definitely a poignant way to show they're no longer eye to eye. A thought: Yuna understood Tidus well enough that I imagine she'd realize how hard it would be for him to be fired, and be angry at him for forcing her into a situation where she had to do that.