The thing about fantasy worldbuilding is that verisimilitude and the rule of cool are not enemies. Someone who looks at a pod of flying whales and asks “what do they eat?” is not being a spoilsport – they’re engaging with the premise. There are any number of much more serious objections to aerial megafauna than lack of any obvious role in a trophic web that could have been raised if they just wanted to shoot the idea down; a person who wants to know what the flying whales eat is all but explicitly yes-anding the idea. Sure, you might not have an answer at your fingertips, but acting like it’s unimaginative for them to have asked is a really fucking weird way to react.