throwing the ability to catch one of the Legendary Dogs kind of pisses me off too, for 2 reasons.
1. Having the first encounter can take FOREVER, and without abilities like Arena Trap, it is extremely difficult to catch them. They are like overpowered Abra. It can be just downright annoying trying to catch them.
2. Giving you one of three Legendaries makes me really angry. It makes it so even if you do somehow succeed at catching one of them, you have to trade and completely start from scratch twice to get all three, which can take an outrageous amount of time to do.
Also, one other thing that really bugs me is Mew. Mew makes completing the Pokedex virtually impossible. I only have FR, LG, R, S, and Crystal. There is no way for me to get Mew. I also only have a GBA SP, so i couldnt get Mew even if i had the right game to do so.