I believe you mis-interpreting me. I'm not an emperor player and you won't see me playing it on my own. Monarch is the level I play on. I've played a lot of SG's (or used too) and when you play games with multiple players, like an SG or a DG, you can typically handle a difficulty level one to two levels above what your comfortable with. With this many players emperor should be a lot of fun and still hold some challenge. Add in the concept of factions/rebellions and it'll keep the challenge there.
Prince IMO will be way too easy and will lose the challenge of the AI's. The only challenge will be faction politics and the game will be a quick rise to domination. If we play emperor, or monarch, we won't easily become the runaway civ. We'll actually have a challenge with the AI's too. It'll keep the civ game fun and it'll add to the DG.
The last DG was on noble I believe and we very quickly took the #1 spot. There wasn't any challenge anymore and we could have picked whatever vc we wanted. It wasn't any fun. I would prefer we have the challenge of faction politics and the challenge of possibly dangerous AI's.