If the servo and esc were plugged into the wrong channels, then the steering would move when you pulled the throttle. He does not have that problem. The transmitter is the only thing in common among all of his cars.

if you can make up the difference in center with sub trim, trim, and link length then make the adjustments and enjoy your radio for what it is, but be aware that the radio will probably start doing weird stuff as it ages. If you have that many cars, a nice radio is a wise investment. That is the only link you have to your car.

Also, Spektrum is only slightly better than FlySky in my eyes, simply because of Horizon Hobbies. I will never trust my cars with anything except Airtronics/Sanwa or Futaba.