I couldn't agree more. They pay me to sell their air and I still advise everyone who asks they should really make their own arrangements. Not only is it a better value to find your own air all the myths about the security of booking with the cruiselines is just that a myth. Insurance is your only protection. I have people call me all the time who say I want to add cruise air because if the flight is delayed I want them to have to be responsible for getting me to the ship.
In the late winter storms I had dozens if not hundreds of clients affected in Denver, NYC and other airports. The folks stuck sitting on the floor of the Denver airport for 2-3 days didn't much care whether they booked air through the cruiseline or on their own. There was no way out and they weren't getting to the ship.
Read all that fine print on your ticket pack or eDocs sometime. It lets the cruise line off the hook completely for any air issues and places the responsibility back on the airlines even if you book air with the cruiseline. You pay more, get whatever flight they want to provide (perhaps multiple stops and transfers) and if you don't like what they provide you can pay an air deviation fee to get it changed. Well... you can if there are any other flight available when they actually book your flight 3 weeks before your sailing. The airlines block space for the cruiselines for air through contract. What flights and routes do you think they block? They hold the number of flights left after everyone else has booked the desirable air. What didn't sell they give to the cruiseline to pass on to you at an incredibly marked up price.
Make your own air arrangements and follow the advice I've seen provided by Dave here a number of times and come in the day before if possible. If not at least give yourself 5 hours or more between arrival and ship departure. Same on the return flight, give it at least 5 hours. If you cruise enough, at some point you be very happy you didn't try to cut things too close.