If Iraq/Mesopotamia was retained by the Safavids instead of being conquered by the Ottomans, how well would it do?
IOTL, Ottoman Iraq was an impoverished hinterland. By 1800 it had merely 1.3 million people, not much more than the population of Sumer
five thousand years before! Historian Tom Nieuwenhuis's description is, well, dismal:
At the start of our period a limited number of urban centers were rather isolated and sometimes threatened from the outer world. In the immediate surroundings of these towns a small strip of sedentary cultivation was to be found, more or less permanently threatened by inundations and epidemics, droughts and famines, wars, invasions or exploitation from absentee landlords, and, last but not least, by Bedouin raids. The rest of the countryside was an area without clear borders, mostly under tribal authority, where the provincial government had restricted or only nominal influence. This area was periodically refilled and disturbed by nomadic newcomers who hoped to find richer pastures or good source of plunder in the fertile riverain areas of Iraq.
On the other hand, had the Safavids managed to hold on to Iraq and attain Ottoman recognition, the region (even with its depleted population of 1.3 million) would make up 14% of the empire's population. Plus, Iraq – with its Shi'ite shrine cities of Najaf and Karbala – would hold far more significance to the Safavids than it ever would to the Ottomans.
So how well could Iraq do under the Safavids?