Honestly, come to think of it. Why not remove lm altogether and replace him with a dragon knight (spell sword, arcane blademaster, swordsage, you know). Someone that uses both magic and fighting. And then just have a seperate mage class that can use both light and dark magics.
If you really want to set TS apart from other AoS, then add some serious depth to the characters so that while each is unique, they also have many different ways to play. Maybe it is a lot to ask, but honestly to revamp the AoS genre and really make a smash hit we would need to make a sequel, not just a repackaged TS (which tends to be what it is right now). I mean it's great to work from the TS1 template, but that game still pushed the boundaries of SC to function as well as it did. Why allow ourselves to get lazy and just copy the same things over?
By all means keep things how they are, but just hear me out. We can keep the action oriented gameplay of TS intact. It's actually one of its defining characteristics. But let's go out on a limb here and start exploring some other avenues. No, not items or equipment that randomly spawns on the map. Let's not just add different kinds of spawn (although we can certainly learn a few things from Hero Sanctuary).
Take for instance, the dragon knight idea. He's a guy (or girl, since uninefested kerrigan with a psiblade attached may be the best model) that fights with a sword as well as magic. So we need to capture this feel of mysticism and ferocity in a single package. He can't be terribly fragile, so first level spell go ahead and make defensive in some minor and personal way. Just go ahead and read through some of the things I came up with for spells.
l1: Dragonskin (passive) -- 20% armor bonus.
l2: Auspex (passive) -- In addition to seeing up cliffs, also gains detection. Vision range is increased by 1.
l3: Furious Blow (active) -- Physical attack damage increased by 100% on the next attack.
l4: Dragon's Breath (active) -- Magical fire that deals 75 splash damage (hellion flame, longer duration, attack speed 0.25).
Passive abilities aren't on a timer, rather they are low cost to activate, but remain active until deactivated or the player runs out of mana. They burn through mana while active, however. In addition, I suggest mana to be separated into into two categories. Arcane potency and arcane stamina. The first would increase, as it suggests, the potency of magic. The damage/bonuses/hexes would be increased across the board by a small amount. For example, in the l2 example above, the vision bonus would increase to 2. Arcane stamnia, on the other hand, is just the typical mana upgrade.
I think the above spells would give someone too aggressive for a spellcaster class (but not as ballsy as a warrior class) a place to slide in. There's clearly a lot of potential for DPS, but there's a balance between that, scouting, and defensive capability. It's really rough, and if I were to develop it more, I would add some more skill synergy.
But yeah, just some thoughts.
None.