Either way, there are no pro-gamers in the twitch-oriented genres that use trackballs. So no matter what, the gamepad/trackball is going to be a handicap. I think we're all just hoping for "good enough", not "as good as a mouse". I'd settle for "good enough". The gap between a mouse and a thumbstick is such a massive ocean that a substantial improvement, even if it doesn't reach "as good as mouse" would be worth buying.
As to pro-gamers, some of us remember when over half of the pro gamers used nothing but trackballs (in preference to optical or mechanical mice). The short story here is that trackballs didn't keep up with the newer laser technology needed for better resolution, so the pros moved on to mice. There are now some trackballs that use laser technology, but everyone (for better or worse) has moved on.
Several other of their ideas are in error. Larger trackballs are not needed (logitech and kesington both make popular trackballs with small radii that perform well. The weight of the ball is also a red herring as it is possible to make lighter balls if needed.
The "issue" of cleaning is minimal and a non-issue overall (ask any trackball user). The idea that circuit space is constrained is also a non-issue. Modern trackballs use a laser to read the ball (a feature of trackballs is no z-axis movement) The circuitry to deal with this is small as is the circuitry for much of the rest of the device.
The real argument is that the material cost is higher, so they'd rather use inferior design and bump up profit margins. Most gamers will pay over $50 for a mouse (with some of us giving over $100 for our mice or trackballs). I'd rather have a quality device and pay a little more.