Why is Fly a "usually useless" move in showdown?

Question

Fly is one of the best physical flying type move by having 90 base power and 95 accuracy and hits a turn after being used. It can also be used after using toxic as a replacement for protect if you prefer offence. It's only downside is that while your Pokemon uses fly, the opposing Pokemon can use a status move but that's not that bad, isn't it?

Answer 1

It’s because of the turn it takes to hit and that there is brave bird.
Most Flying Pokémon with fly ALSO know the superior Brave bird. Brave bird hits way harder and doesn’t take a turn in the air. The turn it takes for it to hit allows the opponent to switch to a better matchup, making a super effective hit near impossible.

Answer 2

The reason why Fly is usually useless is because there are better options. Drill Peck has 10 BP less than Fly, however it has 100% accuracy unlike Fly's 95 and takes 1 turn. Brave Bird has 120 base power and 100% accuracy, which is far superior to a weaker move that takes 2 turns to do damage. Fly's effective base power is actually 45 since it takes 2 turns. Even Aerial Ace is better since it never misses and is technically stronger.