Well, Wailord is the FLOAT whale Pokemon, and snakes can get REALLY long. A quick google search showed me a snake that was 7.3 meters long before it died, and the Guinness book of world records recognizes the largest at 10 meters. Given that they're dragons, which are traditionally supposed to be pretty big, 4 meters isn't exactly a stretch.

If you’re taking the sizes from the anime … the anime REALLY misrepresents a lot of Pokemon.

In general, I’d argue that Gamefreak tends to do their research.