Sounds like the long pike might possibly be useful in battle servers for being able to protect a wider swath of allies from flanking cav. But it may only be good at getting the horse to rear up, though not nearly as good for actually killing the horse once you've stopped it, compared to the normal pike.
I think if this thing takes 3 slots, it should at least be clearly better in its anti-cav role. Maybe at least give it equal damage compared to the pike. With its slow speed and the lack of overhead attack, I think it will be very hard to say that it's as good vs infantry as the normal pike, even when ignoring the lower damage and 3 slot usage. But maybe with equal damage, it might be worth it for support role of protecting the line from cav.