If we're talking about xG, then your point about not needing Haaland or another top striker overlooks a quite major point: While Chelsea has an xG not very different from the other top teams in the PL, they are underperforming that XG much more than any of the others. Leicester and United are 7-8 goals above their xG in the PL, City is just very slightly above, Liverpool is ~5 below and Chelsea are more than 7 below. They are also performing worse under Tuchel than they did under Lampard in this respect: 1.3 goals per game with a 1.8 xG, while Lampard had 1.7 goals per game with a 1.8 xG.
I think it is reasonable to assume that tells the same story as the eye test, which is that they're short of consistent, high quality finishers and that this is a major reason why they are not scoring as much as they should. Which means someone like Haaland would be exactly what they need. City does not have this problem. It also indicates that Tuchel has made Chelsea a better team essentially by re-balancing their game, improving organisation, possession, defence and control. Those are all foundational qualities, and is a great achievement. But, he has not yet made Chelsea a better offensive team, and they have if anything become less efficient, creating a similar number of chances as before but converting them more rarely.
