My favorite Legendary Pokemon is Arcanine. (See what I did there?)
Arceus is in fact the strongest Pokemon.
I think a lot of legendaries is nice, but Game Freak is overdoing it a little.
And Mew IS legitimately catchable with the Mew Glitch. It is also obtainable in Diamond and Pearl from My Pokemon Ranch after you deposit 999 Pokemon and trade an egg for a Lv. 50 Mew.