I have done both and frankly would now prefer (and have booked) a land vs. cruise to Hawaii. Of your 14 days, you will spend 8 at sea. I happen to like my sea days, but if I wanted an extended Hawaiin vacation, this is not it. At best 6 of your 14 days will be in Hawaii and few of those will allow you late nights and early mornings on the islands. What it is is a great 14 day cruise, a whole lot of sea days, alot less flying and a 6 day "sampler" of the islands and ports.
What it is not ,is time to do the Polynesian Cultural Center from opening at noon until
the end of the last show at 10 pm (with a morning tour of the north shore on the way). It is not allowing for 12 hours or more to really appreciate the road to Hana. It is not allowing for waking at 2:30 am to do Haleakala for sunrise. It is not allowing for an all day side trip tp Lanai or Molokai. No way can any island be seen or appreciated in a single day or even with one overnight.
If you have 14 days, Fly to Oahu and spend 4, spend 4 or 5 on Kuai and the balance in Maui. Even after 14 days you will barely have spent enough time to see it all and "veg out a bit " as well.
If you want a cruise, then take the cruise , but if you want Hawaii, stay on the islands.