Fletching, creating an arrowhead (that needs to be small and perfect) goes through way more material than a hand held obsidian blade, you are not necessarily saving on labour switching to arrows, especially as you now have introduced multiple specialized skills that require hundreds of hours of practice across multiple tribal members (the opposite of this, where you go down to a few babysitters to finesse the final code).

But more relevantly the instant bows were invented you're quota of mammoths to kill a day didn't go up to that maximum possible number + 1 (because sales guys). It stayed at 1 per week or whatever. It's not efficiency, it's management's unrealistics expectations of productive output that I hear being complained about.