Oh Boi, Where do I start >:]
Nonpet magsorc: Sustain increase, possibly by making dark exchange instant cast and lowering its returned resources though thats really over kill as it already gives the second half back overtime. Put shields on a major minor system and have it be around 10k with 40k mag, unaffected by resistances but critable and effected by crit resist.
Pet magsorc: Keep the pets damage the way it is on live but rework deadric prey to a stam ability. (maybe take alittle dps from tormentor and give it to scamp)
Magblade. Sustain increase and same change to shield as stated in nonpet
Magden: Needs more dps, Changing ice staff to actual dps passives would help out alot too
Magcro: Again, same as magden this needs more dps. Skulls needs to be smoother animation and timing, if feels very clunky. In pvp it could use more or better non ground aoe abilities to use. Its what really holds this class back in pvp because noone is going to stand in your stupid.
Destruction Staff: Rework ice staff to actualy dps passives to help out madgen and give the other mag classes more variey to choose from in weapon type. Possibly spell pen, with ancient knowledge for ice staff providing a resistance debuff have dps madgen bring something to the table in group play. Change penetrating magic to effect all abilities with a destruction staff equipped and change it to a flat number instead of a percentage. Destruction expert, change this to when an enemy you are engaded in combat with dies. This would also be a good way to increase sustain for magblade and nonpet.
Mages guild: Make meteor faster to make it more comparable to dawnbreaker (Yes ik dawnbreaker got nerfed, all of these changes are in the perspective of the live patch). Would also be nice to see some tweaks to passives so we need less useless buff skills.
Psijic: Work on the animation and timing for elemental weapon to make it more reliable and feel less clunky and more smooth (We all know what i mean, that 1 second you have to hold ele weap for it to actually work).
Apologies to magplar and mdk, i dont actively play those so I cannot comment on areas they are struggling with or provide suggestions
https://www.youtube.com/watch?v=xQtXZfbYhxE