It's not even that Leo's move doesn't matter. He's making the wrong move. Everyone in the Healeb alliance is shitting on Leo as an ally, and he's totally first to go once it's just them left. They've made it very clear they don't value him, and he should be siding with Nathan and co. if he wants a spot in the endgame.
at this point, he seems to have proven to be a flake and i think no matter what he does, he wont be making it to the end. on the other hand, if they can get jessie to change his vote, it could be a wise decision for HIM. as it stands, he could be screwed if he sits next to donny, so might as well make some true allies and prove his loyalty.