He just abused the opness of the class in every aspect against the lowly skilled old crpg community. Going 2hander on horseback is dead.
I kinda resent this. Firstly, if you'd ever played 2hander cav, you'd know that it isn't OP, and never was. Back in the old days (not the old old days), yeah I used plate and a cataphract horse, because (if you remember) it was the time of super archers. Maybe not so much ranged as there seems to be currently, but those archers (think Ozwan or birdman, or Nocti or Replica) were ridiculously accurate. So yeah, I tanked up, to try to avoid dying to one arrow (I usually took 2-3 instead, and my horse took 3-4).
And I used a Sarranid Battle axe at first, but if you remember there was that enjoyable period where archers started getting plated up, so I used Morning Star for the pierce damage (if you don't 1-hit an archer you're usually dead as a shieldless cav player). I didn't use it for the crushthrough, because it's not that useful on horseback - cav has a mechanic that does what crusthrough does anyway - bumpslash.
Anyway, I wasn't the first 2hander cav - there was a Russian guy who I copied (he used sarranid battle axe). Also as Plazek says he's always been 2hand cav (though with throwing iirc) for as long as I can remember.
About the class itself, it can be very difficult to play. Its also very different to playing as lance cavalry. You won't have a shield and you're on a horse, so you become an arrow/bolt etc magnet.
Best way to play it is to stay out of sight and backstab (like all cav). However, its very hard to take on lance cav if you haven't practiced - their lance can thrust faster than you can swing, and they have the range advantage too. There are some tricks you can use against them, but it takes practice. It's best to run away from other cav (1handers will beat you with speed too, and most cav 1handers match your 2hander's range), and obviously if you see a horse archer run.
The best use for it is as a support class. Wait till both infantry sides have started fighting, and run around bumping enemies and slashing them. You won't be doing straight line hit and runs like lance cav, so get a horse with decent manuever rather than a really fast one.
As for weapons, it's mainly a matter of personal taste. I tried longsword, but I prefer the look of the Sarranid axe. All the 2handers currently usuable on horseback are good enough options, though range and speed are more important than damage since you'll get a horse speed bonus anyway. It's also a matter of practice - the more you play with one weapon the more you'll learn it's range and speed and be able to hit people effectively.
Going twohander on horseback will never be dead!