Hello Archon . As a player speaking, unfortunately, most of the time I'm getting purple guardians as well, so I understand you perfectly. The regular % rate is a 25% chance to get an orange and a 75% chance to get a purple one. When there is a x2 chance on the global events, as I understand it, this x2 isn't always applied in every draw we make, as the description clearly mentions a chance, chance means that it is randomly applied.
Keep in mind, that the % rate to get V or IV guardian is applied to every bond we open, and not if we will open 4 holy bonds we will get 1 V guardian for sure. Regarding the type of the guardians we receive, it depends on the % drop rate of every guardian has. Some are very common, others are rare, as everything is in this game.
Every time this event pops up, I see the same posts. The players are right of course, but if we will read carefully the descriptions of each event, from the Developers' point of view, and not what we as players think that it is, because of our desire to have it, it will save us from further frustrations. As I mentioned above, it is my personal observations, so as Daria recommended you, the only official replies are from Plarium's Support.