I think there are several good suggestions up-thread on how to balance this. To my mind though I think this takes the magic out of magic. It just doesn't feel different enough from melee attacks if you can do it at will, with a predictable chance of success for low, predictable damage. That's how longswords work.
I agree. The idea in 1E is that magic options are more effective than mundane ones, but limited in their use. Still, if you want to have low-level MUs be able to use magic more frequently (not necessary in my mind, but some players would want that), there are ways to do it without making magic feel just like swinging a sword. Maybe MM still always hits, and you can try to re-cast "forgotten" spells, but in doing so you roll the percentile dice. There might be risks to the caster (lose some HP or XP, lose the ability to cast that spell until it is re-learned, some kind of Sanity check), or risks of spell misfire (targeting ally, healing enemy, causing wild surge).
The idea I'm considering (if MUs want something to do) is to make them better at melee (like Gandalf with Glamdring). Not too good of course, just not a second left foot. I like Philoptomy Jurement's suggestions too.
Great idea. Nothing wrong with wizards using swords -- besides Gandalf, Thulsa Doom springs to mind. The thief's attack table, weapon selection, and HD wouldn't be unbalancing.
Here's another idea. Give the MU more to do by enhancing his role as Knower of Stuff (like wizards of myth), not just Artillery Platform. Adapt the archivist's Dark Knowledge ability (Heroes of Horror). Add an enhanced Aid Another ability, where the MU can use his action to observe and advise, allowing him to bestow on an ally a +X bonus to an attack, AC vs a single attack, or a single save that round (or one of the latter two on himself). Give the MU the ability to bypass some degree of "+X to hit" defenses due to his knowledge of creatures' weaknesses. This last ability would be most useful at low levels, when the MU does not have a magic weapon. And at those levels, his attack rolls aren't much worse than the fighter's, and he has few enough spells that a physical attack isn't a bad option. Plus, it's useful against golems.