Is it really viable or more like a troll/fun alt build? I always wanted to try out but never dared cuz of throwing weapons upkeep + horse upkeep would prolly dry me up! 
One time I tried and I found it really hard to hit something if I was not (completly or almost) stopped so I raged and re-spec'd lol
Lorenzo's build is jav/lancer. Switching between his war spear and a lance depending.
He's out at the moment so I'll try and answer. It takes a fair bit of practice. If you can hit lighter armoured foes, the damage with the speed bonus can be quite significant. I know I've been 1 shot of my horse by him in the past. There is also the horrendous satisfaction of watching Lorenzo get a good head shot on someone. To do it really well is difficult, like any ranged on horseback it requires considerable judgement of range, your speed, enemies speed, angle and all other factors. And often the javs don't kill...merely wound. But that wounding sets you up for a lance/war spear stab that will likely kill you
From watching, Lorenzo often uses the javs to down cav, which I think might be easier than aiming for inf. But he does get some good kills on inf. If his horse gets downed, he uses the warspear with no shield and is decent at blocking ect enough to do damage with it.
The upkeep isn't so bad. I know Lorenzo uses an Arabian (switched to a rouncey atm for the lols, he can ride an Arabian btw despite the riding req). He did sell an heirloom point, but as far as I'm aware the upkeep isn't any worse than most cav builds.
I've always been tempted to make a build of it in the past. But I love my HA to much to switch for a gen
