My .02 cents...

The type of flying you do has a big impact on how you will behave and react when put into a 121 environment.

Take a 500 hour kid who's been flying well maintained aircraft on cloudless days during training and flight instructing at a puppy mill vs. a kid who's been flying 50 year old cessna's building time flying skydivers or traffic watch in questionable weather and ever-changing conditions (please forgive my run-on sentence.) The puppy mill kid will do great in the perfect sim world and have a lot more problems when unexpected things start to happen in the "real" world. A lot of it comes down to the confidence in your own abilities that your flying experience has fostered in you.