Sorry to be ignorant, but what is the disadvantage to spamming the brothel/inn line? I almost always end up doing it for the happiness bonuses in huge cities.
If you have a general in a settlement along with the Brothel line of buildings you have a chance of picking up a long list of various negative traits, the cumulative effects of which eventually cause said Governor to become so bad that the settlement makes less money, has a lower public order, and has a lower growth rate than if the Governor was not present.

In addition. Happiness causes population growth so Brothels do nothing to help Public Order in Huge Cities in the long run.