You guys have no idea what Mirroring is if you are comparing an infiltrator to stormies and saying its mirrored!
The basic definition of mirroring is when you have 2 factions, with units that are essentially the same but with different visual appearances to keep balance in the gameplay. Giving both factions higher tiered infantry units IS NOT mirroring gameplay, its just giving each side its particular unit with its indivual strengths and weaknesses (and abilities) that add to the strategy.
What i am proposing is the EXACT OPPOSITE. Stormtroopers are squads of troopers that offer much better firepower over normal IAT's, and can take a decent amount of punishment (for infantry) before dying. They are an improvement over the concept of the IAT's, and in general well rounded infantry that can stand and fight.
Infiltrators are SNIPER units that are highly effective against infantry, but not much else. They are 1 man units. They also have some tactically significant abilities. To compensate for the infiltrators high offensive capability, they are extremeley vulnerable to fast patrol units (like speederbikes or 2-Ms), because they have low HP, and so you have to resort to stealthier/innovative tactics to keep them alive.
Both would have similar pricing on the GC map, but they offer significantly different approaches to gameplay. This is NOT mirroring.
PS If you want a good example of a RTS game that mirrored, go look at Warcraft 2. I know its ancient, but the teams had the same units but with slightly augmented stats and visual appearances.