Well in my England campaign with the Timescale set to 0.5 I have some pretty huge cities...

London is one example (the capital) and it's pop is 40K+ and is perfectly happy with the 6 free militia units and no general, or with a general Very High tax is fine...

The we have Antioch and Jerusalem which have slightly larger populations than London and are again controllable but this time with a full stack of militia units in there (even with the distance to capital penlty)...

Now if I had not made efforts to the convert the population to my religion and didn't take care to protect my self from spies than those provinces could easily be quite a problem. Note having even one enemy spy in your settlement has a significant negative effect on public order.

I really do not think squalor is the problem it was in RTW and it will not cause serious problems all on it's own, but it is not completely nerfed either and in a difficult region far from your capital and religion it has the potential to become a problem.