First of all, I want to show off that I recognize some buildings from their look. 1) The town hall is Progressive town hall. 2) There are a lot of Confectionaries (or Large Confectionaries). 3) Gunsmith is past age production building.
The confectionary, I don't know, is it good, is it efficient in terms of supplies/tile?
Now the Gunsmith. I once kept some, too, and use them in lieu of the blacksmiths for "finishing xx production xx times" quests as well as for its original purpose -- supplies. But really, the supplies, while better than blacksmiths, are also negligible when outdated by even only one age. So, one might as well opt to the even smaller sized blacksmiths for quests only and forget about the actual supplies.
In my main city, I now have some (OK only 3) base cidar mills. In terms of size, they are 3x2, just like the Gunsmith. In terms of category, they are special production buildings, just like the confectionary. I have Cidar mill upgrade kits but do not plan to use any. Cidar mill when upgraded first of all its size grows and second of all its production options change.
Another characteristic of Confectionaries and Cidar mills alike, is that they can be upgraded to the current age, so as to be able to not only complete "xx production xx times" quests, but also "production xx times in production buildings of your age / the previsous age" quests. Gunsmiths/Blacksmiths cannot fit this purpose.
So all in all, there is no reason to keep the Gunsmiths.