I think @Cicero has said before (and I've seen this said by lots of Chelsea fans elsewhere on the internet tbh) that Pulisic is most likely more of a long term replacement for Willian/Pedro. I think given his stats last season and comparing them to Hazard's, expecting him to pick up that same sort of contribution is unlikely. But I think that he'll have a better season than his last year at Dortmund - and because Hazard is gone and because he was so important to how they played... those goals will have to be replaced and my guess is they'll probably be spread around the team more. So no one player will really be replacing Hazard, it'll take a team effort to come close to replacing him. If Chelsea play well, I suspect Pulisic will get his share of replacing Hazard's contribution - but I suspect that it'll be spread out amongst the other Chelsea attackers as well.