So magic isn't killing enemies quick enough because they've leveled beyond what my magic skills are. If Major Skills existed, lockpicking would not be leveling me up, which would help keep the enemy's improvement from out pacing my own.
...and then it spirals with more skills:
Because I sell the loot I find and everything levels me up, my selling good are making enemies tougher for me as well. So now enemies are tougher because I picked locks and buy & sell goods, but my magic skills are not keeping up because only part of my level increases are due to increases in magic. Unfortunately, magic is weak so mages are really treading water to begin with.
Now those enemies then inflict more damage due to my lockpicking and shopping so I need armor because my magic skills are being outpaced, then my armor skill goes up because magic is under powered and not keeping up and therefore enemies are coming in and landing more blows. Since magic isn't killing enemies in a timely manner and they're right on top of me, I have to switch to melee weapons, then my weapon skills go up and level enemies higher. Now the enemies are leveling from picking locks and shopping and weapon use my mage would prefer not to need in the first place and magic skills are getting further and further behind the curve.
...eventually, my poor mage comes to the realization that she's not a mage anymore and it all started to go downhill when she picked a lock.
[...or was it when she bought the lockpick?]
As a strict mage, you have 6 skills, your racial power and shouts at your disposal.
As a strict fighter, you have 6 skills, your racial power and shouts at your disposal.
As a strict thief, you have 6 skills, your racial power and shouts at your diposal.
A skilled mage/fighter or thief would be able to use those 7 things to great effect if they spent more time worrying about their game than complaining about what their character wouldn't use. Unbalanced? I don't think so. So Skyrim is missing a few things from Oblivion, but it's got just as many, if not more, things to make up for the defficit.
No one is forcing you to do things outside of what your mage will do, so really by doing anything you don't want to do is a cop out of an argument. You have spells that decrease enemy stats and increase your own, you have staves to enchant with multiple enchantments, you have summons. There is no reason to refer to magic as underpowered or unbalanced

