Landorus was always attack-based. That's why it got an increase in attack.
While Thundurus & Tornadus were both equal, stat-wise, Thundurus benefited more from the special spectrum than Tornadus.
Meanwhile you're using a completely different Tiger vs Dragon thing (and citing tv tropes why are you citing tv tropes) even though if you were going solely with Celestial beast you already had an out with Dragon vs Phoenix.
Next up, why wouldn't Landorus be the Turtle in the first place? The turtle is aligned with Earth, longevity, and worship, things that all fit Landorus pretty well.
It could be true, I suppose, but personally I think they just chose some random animals for the sake of it.