A 1/5 hit in revenue might have a larger impact on profits. It would completely wipe out many businesses with small margins. Are we saying that those businesses should not exist?
Edit: increased productivity needs to be a huge part of the argument here
First off, if you want that profit back, hire more people. Unlikely that labour is 100% of your costs. If it’s 10% of your costs you’d have to hire 1/5 more people, and costs would go up 1/5*0.1 = 2%
If your business dies at a 2% loss of profits, i’m ok with that.
But frankly i doubt you’d lose 1/5 of your worker productivity by cutting hours by 1/5 (assuming pay rates stay the same) - so that’s a worst-case scenario where productivity is directly tied to time-spent-working.
Edit: increased productivity needs to be a huge part of the argument here