Might be an unpopular opinion. But I really think people are unfair with Havertz.
He was super good in Germany. Then he joined Chelsea, and they played him as a lone striker, which is neither his position, not a position best suited to his qualities and style of play.
Then Arsenal buys him, to play him... central mid. Which is definitely not his position.
Havertz is a right winger. He can play as a (very) offiensive mid. But he is NOT a lone striker, and he is NOT a central mid in a 433. Now the problem is, he wil have lost his confidence. Like Werner, who can not find it back, even being back in a very favorable context. When confidence goes, you never know if it will come back.
I'm not saying it's impossible to be good in those conditions. But he gets way too much heat considering all that. I don't see Bellingham playing right back or Kane playing left winger. Clubs should buy players to play at their right position. As soon as Arsenal bought him, it was said they wanted him to play CM. That makes no sense. And maybe he'll be a good CM one day. But you can't expect someone to learn a completely new position in so little time while playing against Premier League teams. You will get exposed in those conditions.
If english clubs were more caring about the players they buy and how to play them, there wouldn't be so many failures on the transfers.
Havertz is a fantastically skilled player who suffers from not having a "best position". At Leverkusen, he played on the wing, as a 10 or second striker and eventually was given quite a free role once he was established in the team. So now, he's not really suited to any one particular position and will likely only thrive if a team is built around him.
Werner had a slightly different problem, in that he had too specific a position at Leipzig to thrive elsewhere. He was partnered by Yusuf Poulsen in a quite unique high pressing 4-2-2-2 system which perfectly suited his skillset.