you are correct - Carnival uses the term "Destiny"-class only. However, that is nothing but a marketing statement. Marketing usually simplifies things in order not to cause confusion because people have to remember more things than at all necessary.
Another example is Royal Caribbean's "Vision"-class, which does actually not consist of six sister ships but actually of three pairs of sister ships ("Legend" & "Splendour", "Enchantment" & "Grandeur", "Rhapsody" & "Vision") which are far from being identical to the other pairs and which were even built by two different yards.
So, from a marketing & sales perspective, you are correct - from the technical perspective, I am.