The idea of even a ton of horse moving a phalanx is a bit far fetched. The man on front didnt need to take the full force of the impact from the horse. He was braced and held by 2 men behind him, and those 2 had 2 others holding them. By the end of the phalanx the horses impact has been split and absorbed by dozens of men.

Not to mention a 1,000lb horse, who's then been armored, and has a fully armed and armored rider on top. Is not going to be able to charge at 20mph. 10 mph maybe, but even then it's unlikely to hold that speed for long.

Even with that momentum at 10mphs with a around 1600 lbs of wieght behind it. Your forgetting the basically laws of physics, if you hit that 1 micron thick pointed stick it will not snap immediately. It's going to impale the horse, go many inches deep then snap and remain inside of the horse. If you think that wont stop a horse dead in its tracks your mistaken. Once that first horse is stopped the rest behind it are going to stop, and quickly.

Charging spear points has never been a good idea. Which is why it generally never happened.

As for the OT, it's kind of a cheap way to win. But an exploit, no since it can be broken quickly with high mass troops.