I know what it's used for, but you can't just ignore how clinical the players in the goalscoring positions are. The point still stands that if you had Van Nistelrooy, Batistuta or Romario one on one with the keeper they'll be more successful than Nunez or Weghorst for example. It's not even debatable.
Salah is of course a great goalscorer, but equally he is their most creative player in the front 3. He can't finish the chances he's creating. The other forwards they have all have 1 in 3 goalscoring records in the PL, pretty good but none of them are exactly clinical. The data over an extended period already shows that that is pretty much their level, there's no guarantee that they will have the same amount of chances and suddey convert more of them. That's where fans always seem to misunderstand xG, more chances doesn't always mean more goals will eventually be scored if the players simply aren't capable in the first place. Are we suddenly expecting Anthony to score 20 goals next season just because he always gets into good positions?
For what it's worth, I think United will have even bigger goalscoring issues this season even though the midfielders do tend to chip in a bit more than Liverpool's. Hopefully our defence will be strong enough to make up for the lack of goals.