I don't think musketmen are the real problem. The real problem is the fact it's so easy to beeline to either chemistry or military tradition, you can get a powerful unit far too early. By the time musketmen come around grenadiers and cavalry are just around the corner, so people aim for them, and totally skip out musketmen.
I think rifling should be a prerequesite for both cavalry and grenadiers. Cavalry are supposed to be mounted riflemen anyways. I can't see people firing flintlock muskets from horseback. They should be pushed back in the tech tree, so it's impossible to get cavalry without rifling. It should be the same for grenadiers. Grenadiers are the counter for riflemen, so it doesn't make sence that they come before riflemen have been invented.
I think rifling should be a prerequesite for both cavalry and grenadiers. Cavalry are supposed to be mounted riflemen anyways. I can't see people firing flintlock muskets from horseback. They should be pushed back in the tech tree, so it's impossible to get cavalry without rifling. It should be the same for grenadiers. Grenadiers are the counter for riflemen, so it doesn't make sence that they come before riflemen have been invented.