I'm a military guy who flies commercial all the time, and I have over 1500 hours.

I like the 1500hr rule. Is it arbitrary? Absolutely. The difference between the 1400hr pilot and the 1500hr pilot isn't significant, but the difference between the 250hr pilot and the 1500hr pilot is. The point between 250 and 1500 that the lightbulb moment happens is different for every pilot, but there is a moment. There are lightbulb moments after 1500 hours, too.

The reason why I like the rule is that piloting skill is a quickly perishable skill, and it's dependent on a lot of factors that on any given day can make you half as good as you usually are. If the captain is half as good as he usually is... maybe he didn't get any sleep, his schedule is off, he's got serious personal problems that are distracting him, or he's sick... the FO is the next line of defense against possible disaster. I like knowing that he's at least as experienced as the captain who's not quite performing up to par and not some guy who just happened to meet the mins.