I don't see it as elite. I see it as a skill and mindset issue. The CF is usually the focal point of an attack. We've had many such as RVN and Cole who were elite by any definition, but the way they played the position is what we lack at the moment.
I've always seen the role of a 9 as mostly operating in the box. This needs a certain sort of character and you can see similarities in the most successful number 9s in their prime - Benzema, Falcao, Ibra, Toni, Cavani, Lewandowski, Suarez, Shearer, Cole, Hugo Sanchez, Batistuta, Gerd Muller and pre-fat Ronaldo. But if you also look at players such as Vardy and Defoe, they did their work in the box mostly.
All of these guys put fear into defenders and generated confidence in their team mates, which encouraged them to get the ball to them in goal-scoring situations. They were reliable, quick to react, strong, aggressive, hungry, they bullied the opposition and above all, they wanted the ball in the net. They were also predators with a skill set to match including the ability to head a ball into the opposition's net.
Neither Martial nor Rashford play this way and I don't think they can adapt their game sufficiently. Greenwood? Maybe but for whatever reason, Ole doesn't want to give him a proper run at it.
I'd love to see a front three of Martial, Rashford and Greenwood terrorising defences but at the moment, it feels a way off and realistically, without a steady stream of goals from them, our title challenge will be made harder.
Personally, I would bring someone else in this month, even if only as stop gap cover for the rest of the season.