I think City being a great team plays a good role on this as well, Haaland is amazing but you can't put Haaland at a team like Everton and expect him to get the most goals in a season, that would not work, they do not get enough scoring possibilities.
Of course you are correct Haaland is a very good player, he is one of the first Bundesliga player to come English league and perform the way he does, he is actually one of the best striker on premier league that scores almost all there matches.
However like you said Haaland can never be at a club like Everton because his chances of scoring the way he does on Manchester City will no longer be there because his performance was dependent to the kind of tactics Manchester City has so going to Everton may be very difficult for him to cope.
Behind Haaland's success at Man City cannot be separated from the expertise of a good coach, namely Pep Guardiola. And apart from that, Haaland is also helped on the field by the quality midfielders that Man City has. Without these two things, Haaland would not be where he is now. Currently Haaland is still the top scorer in the Premier League with a total of 9 goals in 9 matches. The second position is occupied by H. Son and the third position is occupied by M. Salah.
This means that Haaland is still the best striker currently in the Premier League. And I think that will continue even until the end of the season. After Man City's mainstay recovers from injury, Haaland will get the best ball supply again in the attack line and score more goals.