I'm a pretty low-time pilot, but have gotten the chance to sit right seat in some turbo-props and gained some invaluable experience there. Its a whole different type of experience than I've gained through instructing in the 152 that I've been instructing in. Different weather like storms, icing, and approaches down to minimums; experience dealing with busier airports and airspace; more advanced aircraft and basic CRM.

IMO (and this is probably an unpopular opinion), just having 1500 hours in mostly 152/172/PA-28's in almost or all VFR is not going to necessarily a better airline pilot. There's got to be a point where instructing experience gained in trainer aircraft somewhat plateaus and doesn't not really transfer over to making a better airline pilot. There are going to be pilots that just don't get opportunities to fly in much other than basic training aircraft, and there's got to be a point where reaching a magical number of hours in the logbook does not suddenly make them ready to haul 50 pax around in a jet. That is where better training at the airline level comes in - training in the type that the pilot will be flying.

On one hand, it is ridiculous that there have been pilots hired with 300 to 500 hours or even less- I do believe pilots in that stage of their career are still in a learning phase. On the other hand, I personally think a 800-1000 hour minimum is more reasonable than 1500 hours and an ATP.