First of all, I want to thank all you guys for the answer and wonderful support. It was nice knowing there are plenty of people out there experiencing the same issues.
Now, to put it straight: Coil and Extreme Primals are the *ONLY* truly challenging endgame content in the game, Extreme primals less than Coil. EVERY other content (4-men dungeons, Crystal Tower) is tuned at a low level of difficulty for people just to blow through it. I play MMOs for 10 years now, having been leading raid groups for 4 or 5 years. Ever since I left my previous game, in which I leaded a group that raided once a week on saturday mornings, I've been excited about doing the same here. Now, I've tried to form a static, I've tried to join and create SEVERAL groups in PF, and the results were always similar to the ones related here.
What I think this game needs is some sort of cross-server grouping implementation. World of Warcraft is anice example of this implementation, where people used that game's feature to friend and invite to group people from other servers to implement communities such as
http://openraid.us/ where people form groups, discuss in forums and schedule raids across all players. We are walking to a point where MMOs are breaching that "realm" barrier, as it isolates players from people who they could be playing with.
I really think there might be enough people out there to nicely progress on SCoB, however most of those are stranded from each other, in different servers or timezones, and they don't have the means to meet up.
Just to get some reality into this post, 5/8 people means 5 people sitting around doing nothing in Revenant's toll for hours (literally, if the missing spot is a tank) while waiting for 3 people who may or may not come, and if they come, who may or may not ("not" more likely than "yes") stay for longer than 2 wipes.