The Fire Nation ships are based on the design of the IJN ships in WW2, particularly the Yamato. For the Case of the Royal Sloop, I find it funny that they gave it a literal pagoda mast as this design feature on Japanese ships in WW2 has been the source of much ridicule and mockery due to them being so awkwardly and comically tall. The most notorious example of such mockery being towards the Fuso class battleships.
Yeah I see some criticism of the idea but no mention on whether it was an actual design flaw or not. Most of the IJN got sunk and all but I’m not aware of them tipping over or anything…