I think they reduced the damage because you really didn't need any power strike or WPF in polearms to use a couch only lance. Now if you have power strike and WPF in polearms, it's going to increase the damage done by these lances.
I usually 1 hit people with the great lance before the nerf, but there against heavy armor and high HP players, I wouldn't 1 hit kill them (especially not if I was on an armored horse, aka slow).
I personally wouldn't recommend using the great lance now that it's been nerfed, but that's just me. You're much better off thrusting a heavy lance or lance.