I really like Havertz and think he'll be great in this Arsenal team.
Transfer after transfer Chelsea keeps making even less sense, their midfield and striker options are horrible.
It would be better to be at Arsenal than Chelsea, Kai Havertz has chosen the best team this season (despite not getting the EPL trophy) because Arsenal have been quite great in the previous season and Kai can show his best performance in the team now.
I assume it is Chelsea's failure they are back chattering so many players in this transfer season.
People might think 'OK, they will buy a few players' - sure, they might. But they cannot bring quality players without CL football so I don't expect them to fill these spots (Havertz, Kovačić) with better players.
Usually quality players will look at the Champions League competition. It will be a little difficult if Chelsea want high quality players, but I believe they will get it if the offer is bigger, but basically European players always want to appear in the champions league, for that Chelsea is now not do any competition in Europe.