The game does not want you to do anything. You just have an overwelmingly but ultimately pointless desire to for some reason finish all the quests you pick up. They're not going to hurt if they just stay in the log.
And you do have to infact use magic to finish the mages guild questline. There's no way through the Labarenth without it.
Of course it's not realistic to be the head of every guild at once. Why do you feel the need to play that way? If you don't want to, you really honest to goodness do not have to. What is unrealistic is expecting a company to create a magic system you literally have to spend in game years studying to even be able to cast a simple fireball and have said company still be afloat to make dlc.
The game design clearly nudges into different questlines. It doesn't make you do it, but it really encourages you to. And yeah, I don't like starting a questline and leaving it hanging. I'm far from alone in that - a lot of people don't like having a quest log full of unfinished stuff. Like I said, with the mages you
have to start the questline to complete another quest and either leave it hanging (when that quest is telling you it involves something really important) or follow it through to the end - in which case you'll end up being archmage. You can bypass the thieves giuld, but the game really pushes towards it and
gives you the impression if you fail the initial speech check with brnjolf (sp?) you have to start that questline to get the info you need to carry on the main quest. You can bypass it, but the quest log leads you to believe you can't.
It's simply a personal preference that I'd like it if the game asked you to choose a guild and stick with that guild, maybe coming into conflict with the others. As it is it's "oih right I'm archmage. Cool. Now I'll go be boss of the thieves guild too. Then I'll assassinate the emperor, become a bard and then take over the Companions". I'd much prefer it if you had to think about what your path is and make a choice. It just seems stupid to me that you can end up with one person running every guild there is. Or at least not be pushed towards actions that might be very out of character for the character you're playing. It's not about having to do magic, the point was about shutting someone who wants to play a pure warrior who never uses magic out of complteing an unrelated quest (they've perhaps already completed half of) with a decent reward unless they go join the mages college. Why is that apparently so difficult to understand?