Hoenn is about half water and half land. Which is what annoys a lot of people.
You also have the large gap between Petalburg and Dewford and then again from Dewford to Slateport. Almost all the extra exploration areas on on the water routes as well.
Lillycove to Mosdeep is just one straight surf to the right. It isn't until after defeating Tate and Liza that you have to surf a lot to do things for the story, which is between the 7th and 8th gym. And it's not that bad. I mean what's the difference between surfing on water and running on grass? You're still fighting trainers, encountering wild Pokemon (albeit they're all water types), and still able to use repels.
Although yes, post-game exploration may amount to more surfing, but the main game itself doesn't have too much.