Eastern Europe was poor and far away in the MA. The poorests were the Baltics, Scandinavia and Poland (not to mention the steppes, ofc). Russia could have been a bit better off at some places but it was sparsly populated. Getting resources in this situation was very problematic - and this is reflected by corruption.

Chivalry - yes, you're right, I've got the same feelings. I will mod and balance the points for StrategyChivalry and BattleChivalry (as I'm doing it with the economic traits). Thanks for feedback, it's exactly what I need.
Besides: sacking and exterminating is a problem and will stay like this. If you exterminated, you won't have high chivalry that attracts new citizens. It's a trade-off.
The Muslim world was the most populous and urbanised in the Middle Ages - but the changes were small in this period (urbanisation moved from 6 to 9%), while in Western Europe it jumped from 1% to 12% (or so, iirc). So the upgrades should be much lower compared to the Western and Eastern Europe.

Controlling lands on the outskirts should indeed incurr costs, imo. It's historical and it made some factions simply not trying to expand (think of Byzantium - they extended domination over parts of Armenia (in broad sense) at times, but it was not possible to control it). Painting the map is not something I'd like to see in SSHIP (even though Alavaria painted the whole map in 199 turns with Pisa in SSHIP 092).

I'd love to have more events with the effects you've described in the SSHIP. If you can help us - you'd be warmly welcome.