I think we can trust Taito's engineers and designers to know what they are doing...
Pedals might seem odd, but my guess is this they are simply for strafing left/right. I could get used to that.
Trigger stick is obviously for aiming and shooting. The other weird control is for forward/back and turning movement.
It also possible the pedals are for turning while the left control is strictly left,right, forward, back. If so, the pedals would allow for varying turning speeds.