In 1e...
Very few people even attempted a single classed M-U from 1st level, and those were often unsuccessful. I can't recall one getting up over 6th level 'honestly'. They required significant DM help to be survivable at low levels because their AC sucked and they needed fairly rare items to improve it and they never seemed to get beyond the point where 1 lucky hit would drop them. Constrast with a fighter which could probably afford plate and shield by 2nd level, after which time few hits would actually hit and several hits would be needed to drop him from any likely foe. Once you added Weapon Specialization into the mix, his average damage output was probably higher as well.
When I played a single classed M-U (which was rarely), I do remember ducking behind the other players and throwing the occasional dart just to be semi-productive. At most levels your main purpose was 'crowd control', primarily with the goal of preventing the party from being surrounded. So you typically held sleep, web, and latter the awesomeness of fireball for situations where the party was outnumbered by 2:1 or more. You could also supplement this with a few flasks of burning oil, and hopefully early on found some combat wands.
Your secondary purpose ended up being casting 'Detect Magic' and latter on (when you could afford the reagent) 'Identify' so that the fighters would know what junk to haul out of the dungeon.
M-U's that went hand to hand typically didn't last that long IME. Hitting something with a staff or dagger (preferably a magic one) was more of a last resort sort of thing, unless your DM was gracious and let you use your staff like a polearm to poke monsters on the other side of the meat shield (which had a really low success rate anyway).
All the higher level M-U's I'm familiar with were actually dual classed elves, in my case a thief/M-U. This didn't significantly up your combat ability, as the wider weapon selection and extra 1/2 hitpoint per level only went so far (thief attack progression was then closer to wizard attack progression in 3e), but it did give you a much easier route to adequate AC at low levels, and much more to do out of combat which alleviated the potential for boredom. And, by the time your thief abilities would largely stop being relevant, you started picking up significant enough M-U abilities to compensate (invisibility, fireball, polymorph self, etc.).