I did look at the turets mana and with the first buildable AOE turet it deals very little damage and can only shoot 2-4 shots before relaoding due to each shoot using 5 mana.
Diver
Drivers build verchial is somewhat werid that it makes a tank then it makes a less hitpointed mech ontop of it not being upgraded every learned lvl of it.
When you use build verchial ability a diolog should appear with a choice of verchial and mana cost of the verchial next to it.
Then the driver should start building the verchial over a period of time which varies depending on verchial and lvl of spell.
As you lvl the ability up the verchials he builds/has built improve in hp, attack, range, and armor.
Also more mechs that he can build would be nice especialy more tank type ones (low speed, decent damage, low attack rate, Hudge HP).
As for his built helecopters are usless as a combat unit.
He should have a simlar thing as with the verchials, with his helecopters.
Also more air units would be nice (lots of helecopters and planes).
Medic
Medics suply plane ability should not only be a shop it should drop some basic suplys for free that improve with the abilites lvl.
Suplies like batteries, healing items, damage upgrades, turets (at higher lvls), baracades, and light verchial(near max lvl of spell).
The plane it self should have a basic weak defence (onboard Air2Ground machineguns) while it is hovering about.
The medics generator spell should have a bigger AOE and not recharge the medic that cast it.
Instead it should have a mana capicity that it slowly fills. That mana then, when the generator dies, goes to the medic that made the generator.
The mana capicity of the ganarator should increase from less that it cost to make the generator to 500 mana regained (which 250 went to building it in the first place)
You could also make a new hero called robot.
The robot has high HP and high mana and is a melee fighter and has some mana regen rate without any abilites.
The spells it could have are
Energy Shield
Mana shield that is changed to absorb some (Not 100%)of delt damage to the robot with a improving effency.
Internal Generator upgarade
Enhances the mana regen rate of the robot drasticly (at high lvls he has a decent regen rate)
1-3 mana regenerated a second should be enough.
Nanites (or Nano Bots)
Alows the Robot to self Regenerate at a quick rate.
Mini bots
Makes a number of Mini robots for a decent amount of mana.
The number of theses bots can be infinate but they are realitavly weak (Power of the mini bots and number created per use increases).
Hardware upgrade.
Upgrades the robots hp, mana, and attack.
In game use. The robot is a tough melee fighter able to make extra helping bots. It relies on tanking and absorbing damage and to help do this has a shield that can absorb some of the incoming damage by draining some of the robot's mana.
The robot has decent hp and mana regen rates so that its shield can recharge at a decent rate and it doesnt die easily. The robot can not hit air.
Note theses are some sugestions and you do not need to use them.