I understand Williams has been mainly playing KPF with a chop out in the ruck. I really like the idea of giving him first go in that role and see he could be a real weapon.I am not opposed to your general line of thought (i.e. that we don't have to play one of Hickey/Vardy/Williams).
But I wouldn't have Jack doing any ruckwork outside ~30-40m from goals. Although he has proven to be a beast and can ragdoll 200cm+ ruckmen, we can't afford to have him pushing down the ground to make ruck contests; we need him on the end of it.
So who then does the rest of the ruckwork when the bench is getting wrecked by Nic's sizeable behind? Allen is really the only option and it is a big ask. Although he did have a fair few hit outs last year. Keys - has Allen been training any ruckwork this preseason?
All things considered, I'd be inclined to give Williams a crack round 1.
Whether it is Oscar or Williams, they will need to be coached so as to be not competing and bringing their man into the contest against JK and JD.