I think the best way of thinking of this is, if you keep dose, grind setting, grind temperature, brew water temperature, volume of water (volumetrics), pump pressure, and tamp pressure constant (and that’s a big “IF” …) then a lower water debit will result in a longer shot time. And you’d probably grind coarser to compensate. Depending on what other variables you kept constant if you wanted shot time to be static, there’d be a point where water debit would be too low to get favorable results in the cup.
I’m all about bell curves at the moment, so I’d say that 200/280ml / 30 sec is somewhere at the top of an optimum water debit curve. 80/100ml I think would be on the wrong side of that peak.