I think it's sort of reasonable in this case, given there's very little investment in running on 4 limbs, while nation states fund track and field programs to the tune of millions of dollars. That the small number of 4 limbed runners are making progress against 2 limbed runners does indicate it might allow higher peak performance. Of course, 4 limbed runners have probably already plucked the low hanging fruit in performance improvements, but the researchers aren't projecting linear improvement