Yeah I think the morningstar is better than any other 1h or 2h weapon from horse. And being able to use a 2h on the ground is more useful than 1h (if you're not using a shield, which he said he wasn't). The other reason why I think 2h from horse is better, is because you don't need to put points into using a shield, so you can have a build like 24/15 instead of 21/15.
I personally have always been polearm/1h/shield from horseback. Only one gen did I go straight polearm (and was 21/18 instead of 18/18) and I still did pretty well. I think lancer cav is best cav personally. But I see 2h cav doing better than 1h cav whenever they're on the server.