I don't think it's a coincidence that all of Chelsea's strikers go to ****, though.
Werner and Lukaku cost about £150m and they've both succeeded elsewhere.
They're completely different players too, so what's the issue?
They either don’t fit the system, aren’t suited to the league or just aren’t as good as people think.
As these players are at a high-profile club with fans who aren’t renowned for being patient, they get scrutinised heavily and then criticism rapidly spirals, which naturally leads to a loss of confidence.
Just before Werner went to Chelsea, I had a friend who watches Bundesliga regularly telling me that, although Werner has a decent goal scoring record, he is also not very clinical and can be wasteful in attacking positions. He was also playing in an inferior league.
With Lukaku, I think it’s been an amalgamation of things. Firstly, despite his success in Italy, it also isn’t the strongest league to prove yourself in. If you look at Serie A's leading goalscorers, a lot of the strikers aren't particularly well known or are past their best. Immobile, Dzeko, Zlatan, Joao Pedro, Candreva, Giroud and Pedro Ledesma are all amongst the top 10 leading scorers. None of these strikers would be as prolific right now in the PL. So Lukaku doing well in Italy didn't necessarily mean he'd 'improved' during his time in Milan like many Chelsea fans were saying after he rag dolled our 4th choice CB Pablo Mari at The Emirates...
The other thing is that Tuchel seemed to play him as a target man which isn't what he's suited to. He seemed to have more success playing off the shoulder of a second striker and having the ball into his feet so he can drive at defenders. Chelsea also don't have many (any?) creative midfielders, so sometimes when he has made a good run, their current midfielders don't have the vision to execute the pass he wants.
The interview about leaving Inter also didn't help matters and I reckon that has affected the team dynamics, despite his apology. Wouldn't surprise me if he leaves in Summer.