Reading the rulebook at the "setting up the game 5-8 players" I see that you use 16 calamities, all the Major ones (8 tradable and 8 none tradable).
But what I can understand from BGG's rules explination on Adv. Civ. Is that there are only 4 None tradable, and 8 tradable calamities.
Is this correct? So Mega civ for 5-8 players is more meaner than the adv. civ?
In some ways yes - there are more total calamities in play (the 9 ones can be pretty bad).
On the other hand there have been quite a few tweaks and updates the calamities that make them more manageable. One big feature is that the calamities generally do a better job on scaling up - so the larger the empire the more likely you get the really bad ones.
Another thing to keep in mind is that it's generally harder to hit max cities... so that limits the trade cards (and calamities) that get passed around.