There are probably exactly three mythical Pokemon in each modern generation because some focus group has calculated the ideal time period between releasing new Pokemon for people to keep interest, and it's x/3, where x is the time between releases. It's a matter of logic and business sense.
Either you mean x/4 is optimal or it doesn't make any sense
See the problem with that is azure flute was released in japan but shiny pichu wasn't released anywhere it can be said that they intended to but it's unlikely also victini's shiny has existed since gen 5 yet they have not allowed you to catch it that a long time to just hold a shiny form and not release unless it isn't meant to be released
No, the Azure Flute has never been released anywhere in the world. That's why 100 EVs is the max legal on any stat for Arceus in gen 4, it is only available through a level 100 event and you can't get EVs outside of proteins and such