It doesn’t quite, though, because a % buff stacking additively would mean that waystalker could go from 200% to 200+n %, instead of 200+2n %. Every Xth shot refunding ammo, meanwhile, is very much a function of the ammo you have, meaning it’d work far better on high ammo weapons/classes, and is also a Huntsman talent.
Not actually against such a talent, it does what you say, but the choice of which one to take, depending on the numbers, is, as alsozara describes it, rather academic.
That said, a flat ammo buff, directly or through a consumption reduction, would have quite the potential, as there are occasional ammo drops, and sometimes guaranteed crates, and a player really only needs to conserve enough ammo to get to them.
Edit: It could obviously be “every N shots, but only every X seconds”. Then again, limiting scrounger to trigger twice every 3 seconds could also sort of solve its exponential growth, as weapons with high ammo counts usually come through with fire rate.