Kovacic and Mount aren't difference makers.
Kante has struggled with injuries this season unfortunately, he doesn't really drive play from a ball-playing perspective but he generates a lot of turnovers that we can quickly transition into a counter-attack. He's always been at his best when playing for a side that doesn't care as much about possession and instead looks to exploit counter-attack opportunities (Leicester City, Chelsea under Conte, Chelsea under Lampard depending on the opponent).
Barkley is the most frustrating player in the league, tons of talent but whenever he has time on the ball he makes terrible decisions. Every once and a while some magic shines through and he makes a difference, but it's the exception instead of the rule.
Abraham has not been great for quite a while now to the point of losing his first choice spot to Giroud, who has generally been a better option for multiple reasons. Hopefully Werner gives us a reliable goal scoring threat in that position while also bringing some of the link-up play ability that Giroud has. Werner obviously doesn't hold the ball up like Giroud does so well and doesn't have the presence in the box that Abraham does, so there are trade offs either way.
Gilmour has loads of talent but he needs to catch up physically to his ability. He just turned 19, so give him time of course.
You didn't even mention RLC who is getting back to being fit after being off for a year. He was probably our best midfielder last year before getting injured, forced his way into Sarri's side despite not really being a good fit for that system because he was driving the ball forward so well.
Ziyech can play in the middle but I expect him to take over Willian's spot as the first choice right winger. I want Willian back because he's still a top quality player, but who knows there.
Our biggest weakness by far is left-back.