Most 1h have far better reach than the morningstar, you can fuck your timing up and still hit people with ACS, this is far less true of a morningstar which requires fairly well times swings. I prefer to avoid bumping people (except teammates) whenever possible.
Because most 1h have 38 pierce damage at +0? Oh, right, they are swords. Which means:
Most All 1h have far worse reach than the longsword.
You shouldn't compare the morningstar one horse with the 1h swords, you should compare it with the 1h maces/picks/hammers. The best comparison is with the Military Hammer as they have pretty much the same reach. Both can be used with a shield, both fucks up armour and both looks badass. Take the morningstar if you want even more damage and a better weapon on the ground, take the hammer if you can sacrifice some damage for knockdown and better usefulness with shield when dismounted.
I often use the military hammer one horseback, and it's really good. Plays exactly the same as morningstar. True, swords are generally better, but the extra damage from the morningstar or hammer is really nice. Swords are generally better, (shortened military scythe is a beast, btw), but the shorter anti-armour weapons can still be and advantage as long as the rider knows what he is doing.
Nitpicking: "most" 1h aren't longer than the morningstar. There's a lot of short 1hs (all axes and maces, f.ex.), which pushes the average 1h reach to about 80 reach.
With regards to killing horses, lancers have couch, which 2h cav can do literally nothing about. If you do get blocked by 2h cav their is still no certainty of them killing your horse, a small amount of blocking and turning will easily save its life.
Completely agree to this, though.