Come back report my result.

Yes it is a problem of a combination of drive train, power/torque and electronic.

Now I updated to an integrated 4ch ESC, and a hobby level receiver, the start up is much smoother.
(Nobody understand how henglong's claimed a 8-bit speed control is such bad (assuming 256 levels).

But anyway, HL stuff is out, noticed one more thing: My right drive is much stickier than my left. It was noticed before, but with henglong's not-so-accurate control, it was not obvious. But now, I can clearly see right side is always a few clicks slower than left side, forward or reverse. I saw the gear box on right have metal debris and on the left only have oil.

I am guessing, pls confirm me with your experience, since the two side are different built, the variance should be a systematic variance, i,e, everyone must have right side with same issue, and then aftermarket gearbox is the only solution then.