I was more interested in why West Ham specifically were seen as more of a threat given the comparative strengths of the squads.
Utd vs Liverpool over two legs would be a really boring affair. Utd would just sit deep for 180 minutes as Liverpool have so much more energy than them they wouldn't risk actually going for it. And the high press won't work for Liverpool as Utd are happy to just keep kicking it long hoping for an Ibrahimovic header.
Arsenal vs Liverpool over two legs would be an exciting couple of fixtures though as both teams are happy to go for it and play attacking football.