Well, I agree they are different in the ways you describe.
But by the same token, you can't judge Marina by the older ships. Marina is a beautiful ship and the food is sublime.
Crystal is the only LUX cruise line that is not "all-inclusive" which makes Marina certainly more like Crystal than its brethren Regent which is the most inclusive lux line out there.
Crystal also has the biggest ships in the LUX sector, maing them more like Marina.
I think it depends on why you choose to cruise on Crystal. If it is for great food and service, and on a ship that is fairly port active and goes to great places then the two ships have a lot in common.
Granted there are also differences. If you cruise on Crystal because you like formal nights and ballroom dancing then Marina is probably not for you.
I am just saying that if you like Crystal because of the excellent food & service they provide around port-intensive itineraries then Marina is a logical transition for you.
But if you are a "days at sea" person then maybe not so much - but don't sell Marina short yet. They have a beautiful culinary center where every student gets their own "kitchen" during classes, and the same with arts & crafts class. They also have a Canyon Ranch spa, a wonderful library with DVDs and bigger-screen TVs.
Yes, Crystal gets tons of lecturers and has a movie theater, but Marina, if they chose, could also do that very easily. Keep in mind, Oceania is losing one ship and gaining a second ship like Marina is less than a year - then the standard for comparison will be the Marina class, not the smaller ships.
Just something to watch for future reference.