I'm not entirely sure what you mean by this, but if you mean to say that Maya being more comfortable with MC could prevent the bond between Maya and Josy from being as strong as between MC and either of them, that's certainly possible, but not necessarily a problem.
On a throuple path, I really only see Maya and Josy breaking up or forcing MC to make a decision if their relationship degrades to the point of frequent conflict or confronted with a major crisis. If Maya and Josy still like each other, even if not as much as they like MC, they have little reason to do so as long as they feel they're getting enough time with MC. Their bonds aren't in "competition" with each other, so it doesn't really matter if they're a bit uneven.
It would however be a much bigger problem on a non-throuple path though since MC has indicated he's not interested in sharing. In this circumstance, Maya and Josy's feelings are competing with their feelings for MC since they can't express them both at the same time. Under these circumstances, I definitely can see one of them breaking off to pursue a relationship with MC if they feel it's more promising even with much less conflict or crisis to trigger it.