One handed would make the item to OP. Players would start wearing an Arcane or a Dragon defender with it.
Disagree.
I take your disagreement.
I understand why. But stat wise IT WON"T BE OP, if it weren't meant to be made OP. None less, It could be additional feature from Slayer Point Shop, if it's so OP, as people say, and only used to do tasks or kill monsters, not in PvP situations. Monsters are easy to kill anyways these days. Ain't it true, Charr?
You're essentially taking one of the strongest two-handed weapons in the game and converting it into a one-handed weapon (with potential stat drops, but aside from that). Defender would give it a pretty strong Attack/Strength boost, Shields like DFS or 3rd-Age Kite would give you an insanely strong weapon access to good defensive stats, and Arcane would do both.
Stat-wise not OP, I'd have to disagree with you there. I like the idea of a Zamorakian Hasta, but I don't think we'll be seeing it anytime soon.
(And I'm pretty sure in most PvP scenarios, people are going to take a fancy towards weapons with high damage output or strong DPS, correct me if I'm wrong. Something like this would be just a Zamorakian Spear that has access to the Shield Slot.)