You'll get to a commission one way or another if you don't do dumb shit and stay motivated. Air contracts aren't hard to get, prep for the ASTB and once you pass that you're going to flight school.

Check out airwarriors.com.

There's no way to tell you how likely it is that you end up flying jets. There is no set percentage of flight students that select strike every week, month, or year. The vast majority of Marine pilots fly ospreys or helicopters. Even if you do extremely well in training, there's no way to predict if there will be an open strike slot the week you select, after Primary. With that in mind, work hard for what you want, but be willing to work for the USMC as the type of pilot it needs you to be.

Hard work and performance are generally rewarded, but not always. Marine jets are hurting for funding and flight time at the moment, but that may change in the 6-8 years from today it will take for you to be winged (it won't). Your ground job at your squadron will often come before your flying duties, and you may only fly 6-10 hours per month. It is a lot of book work, admin, and study with a little bit of awesome. You would fly far more in the Air Force.