Onyxia is not fun; 3x XP was a mistake (Too High)
Onyxia is just not enjoyable. The XP boost makes me complete zones sooner than expected, I have to abandon quests which would normally guide me and ultimately it gives this feeling of being rushed somewhere, by design.
I then decided, you know what, let me just RDF to get through these leveling stages faster, might as well if my questing progression is getting ruined like this... And afterwards I started questioning when will the new expansions come out? At that point I lost all interest.
Because that's what it feels like, that I am rushing to some sort of next expansion. I am not immersed one bit in the Vanilla environment.
When Onyxia was announced I thought it was going to be a realm similar to Lordaeron with these progressive expansions catch for attracting more interest because Lordaeron was very underrated. People who I spoke to on Icecrown all had a negative perspective against Lordaeron. But I decided to try it out nevertheless because I was mainly sick of the Icecrown ability to purchase lv 277 items from the store for money, which ultimately caused GS requirements so high that would normally be impossible.
And Lordaeron was one of the most fun realms I have come across and I did progress there even further than I could have on Icecrown realm. It was an extremely refreshing experience exploring the world environment, inspecting more details before going through the grindy endgame. The community on Lordaeron was much calmer and friendlier than on Icecrown I can say with certainty.
Basically, this XP boost it just takes away everything, the adventure, the immersion, forces you towards this grindfest, without having any other option because realistically no matter what, you don't want to be completing grey quests. And ultimately the community is more zombified, aggressive, because their task is no longer to have fun and explore the game but to level up as fast as possible, and that is just not fun.