What does 'long assymetric thrust' even mean? Sounds to me like a measure of time! In this context it's non-sensical, they're just trying to confuse you.
In a crosswind situation the upwind engine failing would cause the most difficulty when correcting for the crosswind as you are not only trying to counteract the crab induced by the wind, but also the yaw created by the failed engine. This would only matter if you were flying a type where handling dictated that you had to land with some power applied, which doesn't apply to many light twins. Mind you the coordination required as you kick it straight while compensating for the reduction in power can be interesting for multi engine students.
Even so, the left engine (in a standard US twin) would still be the critical engine as determination of the critical engine has nothing to do with crosswind.