I think the touchpad on the back of the device strangely makes more sense than the touchpad on the front.
Warframe demonstrated this quite well back in the day with the swipe to fire power gimmick - it was near impossible to move + aim + fire a special ability at the same time due to using a swipe gesture to trigger an ability.
with the pad on the back on the device, your thumbs never leave the sticks, and can quickly do the same swipe up, down, left or right while maintaining movement and right stick aiming. and your index finger can be maintained on the triggers.
Of note - this is entirely about the touchpad, and not a front facing screen with touch capability.