The "we're a small park" excuse is rubbish.
Go back 20 years, when the park was (excluding The Farm) technically smaller, and they had defined areas, with portals and signage.
Look at a park like Phantasialand, which is small and compact, and they have some of the most well-defined, high quality themed lands out there.
The simple and honest reason why the park don't do themed lands is because they don't want to. That's fine too, if that's the case. But let's face, it's not because they couldn't.