That sounds like a feature, not a bug. The ability to survive in the front line is a big deal; it takes some actual character build choices to attain, not just a couple spells. As you noted in this thread, a single level of cleric or fighter would get you plenty of AC.
Yes, if a player wanted to multiclass and not play his PC as a straight up wizard, he could shoehorn the concept in. But, it is a PC concept that straight up wizards could perform in at least 3E. Sounds like a bug, not a feature.
). I know that it probably has happened, but then again, Sleep is one of those spells that is either great or sucky most versions/levels of the game. I suspect that we have often tied up single individuals that we have subdued, but I really do not have any clear memories of those events.