Ok. The new great feature of your map is the Magic Critical and the +Magic, which is from the items (And the idea is probably taken from MMORPGs)
Good Thing:
• It does one thing that DotA has failed to do -> Make spells w/ constant numbers scale until late game.
Though I still don't know the proc chances.
Is 8% high enough? or still low?
Is 12% high enough?
Do the items stack additively (meaning 2%+3%= 5% of proc'ing)?
or diminishingly (meaning 2%+3% =/= 5% of proc'ing, It could only be 3.1%, 3.5%, depending on the formula you're using)
or they don't stack at all.
That goes with the Melee criticals too.
These questions will help me to help you balance your map.
Also, do the movement speed from different Boots stack?
If not, you should put something like "Movement Speed from Boots A & Boots B won't stack"
Well, that's an just example.
And for the Heroes.
• Role-wise. Their skills are fine
• Synergy-wise. Different topic.
Synergy is when one compliments or helps the other do its maximum potential. There is Skill Synergy, Hero Synergy, Item Synergy, etc...
• First we need to focus on Skill Synergy.
I'll give one example of Skill Synergy.
One skill is a stun. The other is a delayed small-AoE spell, meaning there is a delay before the effect actually occurs.
They have Synergy. How? The stun could help increase the chances of the AoE spell to hit the enemy and make it unable to dodge the skill's effect.
That's just one very simple example. There are TONS more! Some are just as simple, while some are more complex, which actually makes the Hero more fun to play with.
Sorry if it's long.
Just trying to help.