I have an e-maxx with a MMM 2200kv setup and have also had to replace the rear diff gears twice. In both instances, the rear diff gave out when landing standing backflips with the throttle still on, on 6s, sporting summit wheels and tires, complete set of steel driveshafts, with the slipper locked. Other than those two occasions, I've had no issues with jumps, wheelies, and general tearing up some grass and dirt.

From my experiences, no, Traxxas does not 'suck'. There is the same amount of logic in stating that they don't make their parts strong enough, and that they put too much power in their product. Personally, I'd rather have more power than the chassis can handle and use it smartly than have an underpowered chassis within the same price point. Of course, lots of power in a chassis that can handle it is best, but when choosing two from 'powerful/bulletproof/inexpensive'....
I think arguing that a brand 'sucks' because certain parts can't handle extreme abuse at the max ratings is a bit silly. The fact is electric motors have a much higher torque output relative to the watts/HP, and is near instant, when compared to nitro engines (which is what the diffs were originally designed for). Certain parts could be made better, which is what the aftermarket is for.