The Pulisic acquisition probably won't go over very well for the die-hard Chelsea fans at that price point. That's a decently hefty fee for a good, not great player. I think the move was made for 2 reasons: potential and marketing.
Pulisic will play wing/outside F for Chelsea and should fit into Sarri's system very well. He has the versatility to fill in centrally if needed. What makes him a "good" player right now is his ability to consistently win 1v1 matchups on the wing and successfully deliver the ball. That makes him Willian's equal and superior to Pedro. Wing play in Sarri's system is pretty basic when all is said and done. Consistently beat the first defender = good. Ability to consistently generate dangerous balls into the box = very good. Ability to do those two AND integrate the ability to consistently beat the second/third defender = world class. His delivery is inconsistent but is expected to improve with time. When he had Dembele and Auba, it's no coincidence he looked more dangerous. He won't be solely out on the wing for Chelsea as Sarri gives Willian and Pedro more freedom. That should help his game as he runs well at defenders but also means he's going to have to finish more than Dortmund required of him. People will complain that Chelsea just spent 50M+ on a bench player. I wouldn't get too concerned. First off, Sancho is awesome. Secondly, he declared his desire to move before the season, and coupled with the injury and emergence of Sancho, Dortmund did the right thing. If things don't go off the rails, Sancho will demand a higher fee than the inflated Pulisic transfer. He's that good. Furthermore, Chelsea needed another wing/outside F. Pedro and Willian are on the wrong side of 30. They have a really nice, but untested, player in Hudson-Odoi who they'll hopefully give opportunities. He and Pulisic give them a base for the future. For all the love Chelsea fans have for Hudson-Odoi, Pulisic is much more proven. The metrics support his status as one of the best young players in Europe. He ranked #1 in dribbles in the Bunda last year. What he hasn't not been able to do is generate assists or goals to match his other numbers. The numbers say he's poor defensively but also is very good in generating meaningful counters. So the ability is there to be more well-rounded.
Second is marketing. People get on message boards and talk jersey sales. That's great for Nike, but not Chelsea. Chelsea is like every other big Euro club in that they want America. The world is saturated for teams wanting to increase their brand, with the notable and monstrous exception of America. And the reason isn't jersey sales. Fans = views = corporate money in the States. Nike will go full throttle on Pulisic. NBC will as well. Corporate relations and sponsorships are what everyone is after. Not too many American companies have made the jump and there is a ton of money to be had. ManU has over 400 corporate sponsors. All that money means more to spend in the future. The future ability to grow as individual clubs is stunted financially and really is all about collective league agreements anymore (or making the CL). The one exception to this is America. Soccer is now ahead of the NBA and NHL in viewership in the US. It's #2 in viewership in individuals less than 30 years of age. I read somewhere today that signing Pulisic probably nets Chelsea at least 10M in US corporate sponsorship alone whether or not he actually sees the field next year.
If I put aside that I love Pulisic going to Chelsea as a US fan, I'm probably torn on the signing as a Chelsea fan. I can see why they paid what they did and Lord knows I'm sick of watching Willian up top, but honestly, I'd rather have Sancho. But there aren't too many young, experienced players like Pulisic laying around. I hope Hudson-Odoi isn't miffed at the signing because he probably has a higher ceiling than Pulisic. I do like that Chelsea was proactive. They may be in for a 2 or 4 window signing ban here shortly, so they have to make moves. I view it as a move for the future, as I'm sure Chelsea does with the loan back to Dortmund for the remainder to the season. Chelsea still needs a #9 to improve. Morata has been trash.
Now, let's throw more money at Hazard. Because without him, Chelsea is screwed.