Has any Pokémon fell so far from glory as Flygon?
Gen 3: Flygon is introduced. Despite its average stats, it has a unique typing that allows it to hit the only type resisted by Dragon with STAB earthquake, making it very strong competitively. It quickly becomes a fan favorite
Gen 4: The Physical/Special split is implemented, allowing Flygon to finally be able to use Dragon type moves by utilizing its higher Attacking stat. Unfortunately, Garchomp, a Pokémon with the same typing is introduced. Not only is it stronger in virtually every way, but its menacing appearance and design make it a new fan favorite alongside the likes of Lucario and Lopunny. Flygon's relevancy starts to plummet.
Gen 5: Hidden abilities are introduced, allowing Flygon to possibly get a stronger one. However, Flygon doesn't get a HA while Garchomp does, causing Flygon to further fall.
Gen 6: Mega Evolutions are introduced as a way to breathe new life into old Pokémon, whether it's by making weaker and overlooked Pokémon more competitively viable or making popular strong Pokémon even stronger. Alas, Flygon doesn't get a Mega. However, Garchomp did. And it wasn't even a great Mega either, considering Garchomp's normal form outclasses it. Not only that, but with the brand new Fairy type being a thing, Flygon grows even weaker. But it's okay, because OR/AS comes along, remakes of the games that Flygon originally debut in. There's even a character named Aaron who has Flygon as his signature Pokémon. Surely it would get a Mega this time, right? Nope! To make things even worse, Game Freak pulls a troll by having Aaron give you a Garchompite after collecting 1000 flags. In the end, Flygon is the ONLY Gen 3 Dragon type Pokémon to not get a Mega despite needing one so badly and being fairly popular.
Gen 7: There's a strong possibly of no new Mega Evolutions being introduced, and with more and more Pokémon and a continual power creep, Flygon will only keep getting worse.