The wizards in Barbara Hambly's first couple of series were master swordsmen, but once she got past her Octogenerian Ubermensch phase, she pretty much dropped that conceit - though wizards still trained in combat to learn to think clearly under pressure. The concept of magic being something you can do a set number of times per day without apriciable effort and then you can't do more magic regardless of the effort you put into it is completely against any fantasy I have encountered. Pithy "manage my resources better" comments aside, a magic user who can no longer manage to cast any spells should not be using a crossbow instead imo, they should be collapsed with the worst migraine of their life, drained of physical and spiritual strength from the overuse of their abilities.
Not that I have a problem with magic users managing their resources - but it should be because the time or effort of using magic for a given task is greater than that to accomplish it by mundane means, not because they can cast EXACTLY 3 spells of that level in this 2 hour period.