That's a good signing for you guys, an excellent nod to the future.
Out of interest what model does Chelsea run for transfers? Is it the classic sporting director and coach together or something else?
The last manager to have pretty much full control over transfers was Mourinho back in his first spell, following that it's been varying models of the club driving transfers with or without a DOF (currently without following Michael Emenalo's departure to Monaco) and with varying levels of consultation with the manager.
For Sarri you've seen the club pursue some of his hand-picked targets, Jorginho being the obvious example, and they've also attempted to sign the likes of Rugani and Higuain, players he's previously managed and presumably has recommended. But the club also makes its own moves, Arrizabalaga was scouted when the contract negotiations with Courtois broke down and it became clear we'd be needing to find a new GK. The transfer seemed to come out of nowhere and happen quite quickly, but it was obviously the club's primary contingency plan in the event of Courtois leaving.
According to the Telegraph's Matt Law (one of the most reliable journos who covers the club regularly) we were looking at Pulisic in the summer prior to Sarri being appointed, so he falls in the category of a club signing made with a view toward replacing the ageing Willian + Pedro RW unit. One benefit of Sarri is that he's more comfortable with this model than many managers (Conte, for example, was prone to throwing his toys out of the pram when the club wouldn't/couldn't get who he wanted), as he views himself as more of a players coach and isn't all that interested in the market. De Laurentiis at Napoli recently bemoaned the fact that he'd ask Sarri who to buy, and he'd reply that he didn't care.
"Sarri seemed timid and I discovered he was so dissatisfied with his past (working in finance). For a Communist to base his profession on the evils of money brought him to suffer from a syndrome of dissatisfaction.
"I found Sarri to be very highly-strung. His wife couldn’t even come to the stadium. I used to say to Sarri, who shall we buy? He’d reply that he didn’t want to know anything about it.”
Marina Granovskaia is basically the most important backroom figure at the club, overseeing it on behalf of Abramovich, and personally conducts all of the transfer business and contract negotiations. Following Emenalo's departure she nominally assumed his DOF duties, but he was arguably more a chief scout charged with being a conduit between the manager and the club, rather than a true decision-maker. She's basically been running the joint since 2010, and if we do bring in another DOF in future it will likely be more in the vein of the role I described Emenalo having rather than a Monchi/Marcel Brands/Txixi Begiristain type who oversee everything.