Even if the manager did assume this, it wouldn’t affect her conclusion. Instead, her argument is vulnerable to criticism because she assumes that short vacations are equally as effective as long vacations at reducing exhaustion.

The manager never assumes that vacations are the only methods that effectively reduce workers’ exhaustion. She just argues that workers should take several short vacations instead of one or two long ones to reduce exhaustion as much as possible.

Even if vacations reduce exhaustion differently for each worker, it doesn’t change the manager’s argument that several short vacations are better than one or two long ones for reducing exhaustion. It doesn't matter if some workers experience more or less reduction.

The manager focuses on how vacation time is divided, not the total amount. More vacation time probably is better, but this doesn’t impact the argument that workers— regardless of their total vacation time— should take several short vacations instead of one or two long ones.

The manager fails to consider that long vacations might reduce exhaustion much more than short ones. If this is the case, then one or two long vacations might actually reduce exhaustion more than several short ones.