1500 hours being useful at making you a better pilot is highly questionable in my opinion. Flying GA for 1500 hours might, just might make make you a better GA pilot but could make you worse and you'd be no better at airline ops for it I'd argue. It's not like you have 6 monthly sim checks and line checks in GA. 1500 hours regional TP flying is a different pot of tea, as that's handling practice on a large complex aircraft, exposure to emergencies, descision making and SOPs all in 1500 hours compared to flying to Northern France VFR for a sandwich in a light aircraft.
I think where hours is only useful is keeping a pecking order that assists progression. A better way was the old way, basic CPL/IR for short haul, build up some hours and jet time to allow you to apply for anything long haul. Not for any safety reason, just keeps the flow. It's stopped now though.