You can have 500 or 10,000 hrs and still fail a checkride.

But in reality, less experience before going into a 121 ops as PIC (135 cargo, CFI, banner towing, traffic, you name it) is less experience when you get into the captain seat.

You can get a FO job for any airline, but the experience in the real world alone it will worth the wait, because at the end in a emergency is not how much time you have is how you handle the situation. And the way to handle it is following company procedures and having some previous experience overall.

It's not the same having a simulated engine failure, than a real life engine failure or electrical problem. Plus you have to add how you feel at that moment, did you sleep well last night, is the leg #5 in that last day, etc.