Chelsea potential problem, looking at the first few games, is that Lukaku proves to be less effective then Werner for their system and overall play. Everyone knows that Werner couldn't score to save his life last season, but his movement and ability to drag the defence all around the pitch is clearly superior to Lukaku, so it opened up all kinds of issues for the opposition, especially if they play with a high line. I mean, there was a reason why Chelsea fans defended Werner to some extent despite him missing shitloads of chances.
So, while Lukaku will indeed provide more goals, Chelsea might be overall easier to defend against and a bit one-dimensional which is the problem that all Lukaku teams had so far (Conte can say what he likes, but Inter was easily stopped in Europe). Juventus game was a bit worrying for them in that sense. Chelsea could play them together, but then they lose a lot of their link-up play upfront and it's far from ideal, at least in bigger games.
Still early days of course, but it will be interesting to see how things will pan out as the season goes.