The problem with cottages before emancipation is that you likely gain more science from farms + scientists + caste system + pacifism + great people. Yes it is resonable to build cottages in the capital and run bureaucracy for the gold per turn but doubtful to have alot of them before the renaissances. For food poor cities that will never get a great person (so all gpp is wasted which is a deal breaker for specialists) cottages make sense but food rich cities should maximize their food output and then use specialists to farm that great people bar dry of cheap great people and then we can think about cottages. These food rich cities can be relativly quickly converted into production powerhouses by converting farms into workshops which may be a good idea if you want to exploit a technological advantage. Caste system do add that extra hammer to the workshops. In particular with spiritual you can run serfdom to make the conversion quicker.