It is true the Cavalry are able to defend a lot more area, so ya, I can see that we could need some. I also think getting our core productive - mostly with aquaducts to grow past size 6 as important too - perhaps more so than losing some corrupt town. If we have the aquaducts, then I think a mix of cav and markets works best. I would definitely keep researching at least until steam. Rail will make things easier. We are a bit on the weak size to pump out lots of Cavalry. Rails will get our cities to decent levels of production, so I definitely don't think going for rails would slow the win - probably the opposite.