From what little I've heard about air-sea flight packages, I would shy away from them. They are going to do what's cheapest for them and not worry a whole lot about you either getting there way too early or nearly too late. When they say "they'll try", I wouldn't put too much stock in it. Also, remember the airlines are trying to do way more with way less these days and there are far fewer flights available than even a year or two ago.
Everybody has their own ideas on airfare, best deals etc and I'm sure some will respond who have had good experiences with sea-air packages. I've always belonged to AAA and go in to their travel office to book my cruises. They've always obtained really good flight rates for us where I can't imagine an air-sea package being too much cheaper...Plus they always get us on flights with reasonable times. If you can possibly spend the night at a hotel before your cruise, it's MUCH more relaxing.