If you played more, you'd realize that's really false.
I played a lot, don't you worry 
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The most obvious difference lies in the teir 2 tactical missile launchers, but there are differences up and down the line. Most of those differences are stat rather than role driven, but even there you get differences. For example, an Aeon artillery barrage is fairly accurate where a cybran artillery barrage does massive damage to a wide area... if you can hit the broad side of a barn. Aeon's 'anti-group' weaponry is it's PD (which has a relatively wide area of effect) as a result, while artillery does massive damage, while Cybran's rely on pin-point accuracy with their PD, with their artillery taking on the anti-group role.
I would say that the biggest differences were in Experimentals, but sadly not too many games reached that point. Artillery wasn't SO different as you might think. Basically you built shields, AA MK3s and a couple (or one if you were poor) artillery batteries, and nuke the opponent for some time. In the end the effect of batteries was the same. PDs, everyone knows that Aeon's were good against slow & strong units, Cybran - small and numerous, UEF - everything. So yeah, there are differences and they play a role in the game, but too often either the differences are too small (T2 mobile AA, T2 TML, T3 spy...), or there is too much imbalance (Restorers vs. the rest). What you don't seem to understand is not the plain difference of units (which quite often is only 200 DPS vs. 210 DPS), but their performance in the game. Sure, playing as Cybran you will have different strategy when playing as Aeon, but in the end the difference is negligible - think for example about T3 spies. They have different amount of Health, fuel capacity, sonar presence, etc. But in the end they only work as suicide planes that will give you an insight into enemy's plans (by scouting his base).
You also get the high-end units, where one might have a tactical missile defense, another has shields, and another can reclaim / repair.
Reclaim of Harbingers is a laugh, as you won't use it often due to it's poor efficiency (3/5 of T1). Shield - in theory - are awesome. Fight -> Fall back -> Restore shields -> Come back for some more. In practice, however, you fight till you die, as if you are constantly retreating you are losing units when the enemy shoots in your back - you treat your units as expandable warriors, due to sheer number of them; you won't macro your ass off, just to get a few units back to full shields - it's a game of a bigger scale. In the mid-game (when T2 TMs rule) most players know to cover their bases with TMDs - the only way to use TMs effectively is to catch your opponent with his pants down. In the late-game on the other hand, T2MLs die too fast (and shoot to slow) to be a threat to approaching army. That said, Loyalist's anti-TM is rarely used (not even mentioning the plasma blast which is nearly useless).
And, the most incredibly obvious item, the Cybran have a heavy stealth outlook rather than shields (lack of mobile shields, but have mobile stealth; no T3 shield facility; T2 shields are distinctly inferior in a number of ways to other races).
Yeah, they tried to make Cybran units sneaky bastards, but they failed pretty much, imho. Cloaking is of course used in some games, but shields (all together) are much more important than cloaking. Due to this fact, Cybrans suffer quite much.
The differences are not negliable... they only look that way.
I would say it like this: at first units feel VERY similar. After some inspection, you realize that there are quite a few differences. Alas, in the the end, all the differences are normalized in the real battle.
What I would like GPG to realize, is the fact that this games is of a great scale. That means that people shouldn't care about +/- 5 DPS and some super sneaky tactics. Sure, implement a few units that have special abilities, but make those abilities USEFUL and DISTINCTIVE. Only Cybrans can produce drone carriers (flying/land units that command a group of combat drones). Only UEF can build T3 destroyers (other races have to try fight it with T2 dest. or with other T3 units). Only Aeon can build gunships. And so on... Just make 70% of unit types similar (that differentiate as in original SupCom), and 30% units should be unique (race-exclusive).
