I’m on the pro-200 hour pilot side. To get someone into an airline fresh out of training is when the knowledge is still there and the skills taught are the sharpest. Whilst I’m sure 1500 hours of towing ‘Happy 50th Margaret’ banners gets you very familiar with VFR ops in a 172, please don’t try and say it makes you a much better multi crew airline pilot. Better at weather avoidance, maybe. Better at R/T, arguably, let’s be honest that’s about it.
My skills were definitely sharpest after about 1500 hrs instructing VFR maneuvers, Instrument Rating and Multi-Engine work. Then I quit instructing, joined an airline and realized the hand-eye coordination, the workload management it was all the same game. You were still a newbie on the line, you had to adjust to new work patterns, "you didn't see it coming" as clearly.. Pure flying, is transferable. Being a system operator, a chimp could do.