This is my sense upon the recent updates. Everything that bonuses CHs bonuses Harbors in the same way, including Golden Age Science bonus and CS bonuses. Harbors have much better adjcancy than CHs, earlier double adj card, immune from floods, great admirals are better than great merchants. Better buildings (lighthouses are much better than markets, markets only have 2 gold besides the trade routes, but look what lighthouses have! so as shipyards v. banks. ), also the cost is reduced since we have the +30% policy only work for Harbors but not Commercial Hubs. Also sea trade routes yield much more than land routes. I really cannot find any better points for Commercial Hubs than Harbors. Maybe Rationalism? But even a doubled(you need +3 and 10 pop) market yields 4 gold and is still not comparable to lighthouse. So as banks v. shipyards.