As a lifelong cav/infantry player (I've picked 2h cav because I like playing 2h on the ground), 2h cav is inferior to both lancers and 1h cav. There's really nothing that a 2h cav player can do that a 1h cav player can't do better. Since 2h cav takes a pretty hefty (~25% to both speed and damage) nerf when used on horseback, can't use a shield, and has no real reach advantage on the majority of the 2h weapons useable on horseback, there's no real reason to go that route (unless, like me, you really, really like 2h weapons).
In all honesty, that suits me just fine, as it keeps the number of 2h cav players down and I never have to worry about my class being nerfed. However, I'd like to see some of the old 2h cav weapons brought back for some variety. The bar mace/long iron mace/studded warclub for example, were originally removed because they had crushthrough (almost 100% crushthrough chance when used on horseback). Now that they don't, there's no reason for them not to be used on horseback again.
I don't want to sound like I'm complaining, because I'm not. I like 2h cav the way it is. It's plenty viable, and its ground game is way more fun (to me). BUT, if you take the same player, put them in a generic lancer, 1h cav, and 2h cav build, the lancer and 1h cav will outperform the 2h cav 90% of the time.