Legendary Pokemon (How they could be possibly obtained without eggs)

Hi, first time here.
Sorry for my poor grammar.

I have had an idea for Legendary pokemon to be obtained, this could work for all servers.
In pokemon go, you have legendary raids, where you battle then have a "Bonus Challenge" to catch the raid pokemon. How about if we had pokemon such as Zapdos, Articuno or so, a special event that could happen. Where you and your team can battle the legendary, and catch it if it is defeated in time or so. I may be going off the limits of minecraft. The event could also work in the survival server, with the whole server fighting a legendary bird in one of the many gyms.

May not work out so well, but I just came up with this while training.

 

There was a quest that took a long while players could beat to earn their Legendary Bird for their choosen team. Articuno - Mystic, Zapdos - Instinct, and Moltres - Valor. That quest got taken out as people complained about the difficulty and didnt appreciate getting a Legendary which was already questioned for non-Legend players. Therefore I don't think Legendary Pokemon without a rank will be a thing besides that instance where you could buy Legendary eggs.