1, everything is mostly fine except destruction, without any other skills to support it. The closest to destruction, archer, can function perfectly fine on its own in term of damage and survivability.
2, my conjurer needs nothing but a magicka bar and maxed out summoning trees with perks.
3, its exploitation of game mechanic. Major oversight from developer I call it.
4, impact is OP as long as you have a magicka bar. Once it depleted, you have nothing left worthy of 'defensive mechanism'. Forget those elemental cloak. So of course you got the best defense the game has to offer with unlimited magicka.
5, Game mechanis exploitation to reach complete removal of magicka mechanism is a work around, not solution..
Im ignoring you because you werent able to restrain yourself from using derogatory words repeatedly, which I dislike the most, plus the fact you have
nothing relevant to the thread but decided to jump in nevertheless. To bad this forum doesnt support ignoring, but I ll try my best from now on. Last post to you

1- no, anyone who played the game to minimal levels and content (on master at least) will know this simply isnt true, even them ost independant skill of them all (conjuring, wich is based on spawning creatures to fight for you) will need survival and/or control backup in the 1-20 and 30-50+ ish stages of the game.
every other skill needs to be supported by either 1 or more other skills, all melee builds require support from smithing, any melee build needs support from armor skill and/or block skill, illusion doesnt work well at all on its own, neither does alteration... so on so on... theres offencive, defencive and supportive skills that are needed in synergy to each other.
2-play on harder difficulties and play more content of the game, not even with twin souls (wich you should get only in late stages of the game, unless you are one of the silies that uses console and then plays in the 1-10 levels content and feels "imba") will be enough to avoid you being shot from range, agroed by mobs or your sumons kiled.
3-agree
4-impact needs to be a proc rate I agree, but a mage resorts to downranking of spells to avoid going out of mana or when hes low on mana to keep casting if need be, aswell as staves, enchanted/poisoned daggers etc, a pure mage doesnt mean you can only use spells cast by yourself, you should also have long term buffs from alteration or low mana cost defences from ivnisibility etc
5- agree, yet I have no problems with mana from lvl 30-52 at all without exploiting, its all about itemizing properly, I do run out of manas, but only in very long/difficult fights, to wich I use pots or resort to my dagger staff, while mana recharges.
as for the constant missinformation being thrown around about destruction damage being low
FACT:
a smithing one handed daedriv sword does LESS dps than the base dmg spells (expert) of a destro mage.
two handed and duals, compete with it on long term dmg, but they dont come near destro mage burst dmg potential at all.
melee only surpresses it with exploitation of 3 crafting trees, and even THEN only in single target dps, a mage can sustain high dps on multiple targets.
not to mention specing for alchemy gives you pretty imba pots that boosts your dmg too.