Automatic pollution cleaning works fine with one problem, once there is no pollution left, all the workers are "freed" and need to be reassigned to a task.... great, I can just leave them under my control all the same...
The Idea with the unhappiness is good, probably even quite realistic as a side effect...
ok, true about the oilspills, but these are exceptions, that can be avoided (new ships are much safer)... I mean, look at a city of 5 Million in the turn of the 19th Century like Paris or London, following civ, it would be producing one tile with polution every turn since it has no recycling center...
Mass transportation should be available much sooner, in history the first tubes came at the end of the 19th century...