Just a little suggestion before I’m leaving. Would it be possible to move the research for wall and towers in medieval and the higher ages more close to the beginning in the tech tree?
It’s then possible to get earlier in this ages better defence and they could also be built faster because the better houses will be able then too to get the building time down.
When wall and towers be built at the end of an age then e.g. oil towers from medieval are not really helpful against renaissance or industrial age units. Also all houses are already built with the other buildings from the age and building time is high. The players have then the adequate wall and towers to the units in the age where they are in and can in this way defend their towns more effective.
Another point is too that the players who have no sulphur in their country and may turn down their research before, will be able to build the moat and grapeshot towers in renaissance age.