I don’t understand the Havertz signing, he hasn’t been great for Chelsea so not sure why Arsenal think he’s worth signing. Arsenal need a proper goalscorer, Havertz won’t give them lots of goals. He is not going to be the man to take them to the next level. As a Liverpool fan I am not concerned, then again we have our own problems.
Your perspective of view may not be as true as what the management saw in him that prompted them to sign him. Havertz may not be a prolific finisher, but he can contribute on the field and assist the club create more opportunities. Maybe he was missing some crucial links on the field of play that he can receive at Arsenal. I wouldn't be surprised if he starts doing better at Arsenal than he did at Chelsea.
I think Pochettino is making too quick bold decision since he letting their good players to join other teams e.g. Kante, Kovacic, Koulibaly, Mendy and Havertz. Obviously Pochettino already pick his 11 best players and few good players in bench, but if it's not go like his expectation, Chelsea fans would be very angry.
Ziyech is also among the players departing the club during this transfer window. I'm not sure what he's after, but whatever it is, it should be for the good of the entire team. We can't scrutinize him until the season starts, and we can't see anything helpful in all of the adjustments he's made to the team.