to be fair, Morrowind, Oblivion AND Skyrim (the only three ES single player titles I've played) wandered back and forth across the spectrum of underpowered and overpowered magic, and in some cases, managed to do both at the same time - I know, Impressive right?
Morrowind base magic was *fairly* powerful but heavily limited by a non-regenerating mana pool - This tended to make making a dedicated mage...difficult, as you had to dedicate a significant portion of your character design to finding ways of increasing and/or regeneration your mana pool. However, Enchanting was, in a word, STUPIDLY overpowered, and proper use of the enchantment system to logical extremes was quite capable of breaking the game.
I honestly don't remember Oblivion magic very clearly (it's been a long time, and for some reason, my oblivion experience didn't imprint quite as solidly as my morrowind experience), but based on anecdotes from friends of mine who enjoy breaking game systems, they LOVED oblviion's custom spell creation system, precisely because it could become almost as broken as the enchantment system in Morrowind.
Skyrim, of course, according to most people, swung too far in the opposite direction, and while I found Skyrim magic to be a pleasant adjustment, with regenerating mana pools but significantly scaled back magic power, I know many people HATED skyrim's magic system for not allowing the versatility they wanted AND for not power-scaling appropriately, ending up overall feeling very underpowered.
ESO...is very, very different in it's skill base.
For one - the people complaining about "NOT BEING ABLE TO MAKE NON-MAGIC USING CHARACTERS" are, as many have already suggested, focusing too much on the power source for their powers. They think because a skill uses the mana pool, that makes it a magic spell, and it really doesn't, if you think about it. Mana has just expanded into a catch-all term for "class skill limiting pool". Some of those class skills are *actually* magical, others considerably less so, again, depending on how you look at it.
but, I realize that's not really what you were getting at...
You wonder why you can't currently make a dedicated caster with the particular pool of spell-like skills that you're interested in. The best answers I can give you currently are...
1 - the game's not even released yet...
2 - odds are they'll be including new classes, and quite possible expanding on various class skills and abilities, at some point in the future, so your problem *today* may not be a problem further on down the road - I know that's not very reassuring now, but it is something...
3 - truth be told, and this may sound flippant and unsympathetic, but ESO is NOT WOW. The kind of dedicated mage class that you enjoyed playing, that fit quite well within the world of WOW, may not be appropriate for the world of ESO - I'm not saying it is, or isn't, but the people designing this game have apparently decided on a strange but not entirely inappropriate fusion of Elder Scrolls lore and established gameplay, and the necessary balance and gameplay mechanics that most people expect from an MMO. That was kinda awkwardly phrased, but I guess what I'm trying to say is that you may have to give up on your idea of the classic wow-mage existing in the ESO world - it's possible it'll never be designed that way, either because the devs don't want it to exist that way, or because they can't afford to make something like that because it'd screw up some other balance issue.
4 - if you're really interested in playing ESO, another option you have is start to use the EXISTING character build system, and see if you can't come up with a new way of looking at mages. I'll give you an example...
there's an...interesting...pen-and-paper RPG out there called Deadlands : Hell on Earth. It's this bizarre fusion of old west, supernatural, and post-apocalyptic action-horror RPG genre. I hate it. I really hate it. It's a great game. It's fun, it's innovative, it has an intriguing lore. I hate it. I hate it because I have the hardest time, FITTING my mind around western/supernatural/post-apocalyptic action/horror - it's just too many genres for my brain to handle. I can't really imagine a character I like, because I find myself at war with too many character concepts, too many conflicting themes and stereotypes and whatnot for me to deal with.
But the people that *can*, change their concept of what fits, allow themselves to enjoy a new game with new rules and new ideas and new limits, and create characters and experiences and ways of interacting with the world that they would never have realized if they had refused to adopt a new mindset.
take what you KNOW about mages, what you LOVE about mages, and since you *can't* make them in ESO, at least not currently, the way you'd like - see if you can't redefine YOUR idea of mages. Now, in ESO, you can make a mage that sneaks, and uses a two-handed hammer rather than a staff. He can be a Lizard! A LIZARD!!! and use bows and ride horses and backstab people and THEN set them on fire with the power of his mind. That's a pretty cool mage, too. Sure, maybe you can't teleport short distances and use your AOE damage/stun ability - but you CAN do other things, and they're still magical - you can still call yourself a mage. Hell, my Nightblade can call himself a shadow mage, with his teleporting shadow dagger spell, if that's what I want to call it - now, in ESO, "mage" is mostly just a name, and maybe a bit of a "style" - it's no longer a class quite the way it used to be, and sure, that can be maddening and infuriating, or it can be liberating and amazing!!
truth be told, it'll probably be a little bit a both at times - but that's the best suggesting I can make at the moment...
since you asked