Oblivion was never balanced for pure archetype characters. The best is always a mix. Although why anyone would complain about magicka regeneration for mages when you could have 4-5 magicka restoration potions rolling to give you virtually infinite magicka for a minute is beyond me. People who say warriors were OP on the hardest difficulty.... seriously? Without using alchemy and magic I would break 2 weapons while killing a creature (especially at high levels). My magic users never had any such issues, especially since conjured minions and charmed ones did not suffer from the damage penalties imposed on the protagonist. Thieves were the worst until they hit 100 sneak... then they could repeatedly attack them without retaliation and the attacks would bypass the damage penalty imposed by the difficulty.
Magic in Oblivion (which included alchemy) was just way too useful for any character to not use it... unless you are role-playing a complete mentally handicapped person who never heard of or seen magic throughout the entire game.
You don't have to be mentally handicapped, you only have to be serious about how you role play. There is no mission in the game that cannot be completed by each archetype played pure. Certain things are made more managable with magic, or with great strength, or with great acrobatic abilities or stealth. Certain skills in one field can compensate for a lack of skills in another. That magic may give a few more extra advantages is not all that surprising. It is magic after all. If it didn't allow you to do a few things outside of the norm, it wouldn't be very magical.
But playing pure requires nothing more than will and a hint of imagination. If you decide to play as a pure warrior, who disdains, distrusts and on some level fear sorcery, then you wouldn't do any spell casting. As such, your intelligence and will would remain low for magical functions. You would not be able to cast most spells, because you would lack the requisite skill to do so. You could train, certainly . . . but if you are playing as described above, you would not be inclined to set foot in a mages guild, nor to hold much interaction with spellcasters. You might go into a shop of magical goods to buy something helpful like an invisibility ring. . . you would likely perform tasks for great mages, and for Daedra, to garner powerful artifacts to open locks and to give some protection against magical attacks. But you would not dedicate your time, energy or money to the enhancing of magical powers.
Unlessssss, you decided that you could not be hemmed in by confines and constraints. Unless you could not stand the idea of not having an affinity for magic. Unless you could not bear the idea of other characters having powers, abilities and skills which you do not have, and which enable them to do things innately that you have to find other means of achieving. . . in short, unless, in your heart, you have a hidden desire to be the best, the brightest, the strongest, the most powerful, despite all protestations to the contrary.