I would say its not only in England , Spain or Italy harder to score goals there , its in germany also hard to score goals , just remember when Haaland havnt scored for a few games.
Also it depends on the Team and what kind of other players you have around , mostly it makes the difference if you have good players on your side that making assists.
But we will see what he will doing or if he stay in Germany .
Before any of these transfer talks happened and before any team showed any "real" interest, I always imagined what would happen if Haaland played in Liverpool. Think about it, put mane on one side, put salah on the other side, put haaland at striker, put firmino behind haaland as well like a proper 10 and let them play. At that level you could literally just keep everyone else at defense, because those 4 will end up with finding a way to score no matter what, you would have Liverpool scoring the most goals ever.
Now we know that Liverpool is probably not going for him, but the idea of that is still the same, put that into any other team and you will see it. I do not think that it is the difference between bundesliga or premier league that matters, premier league is the place that had 9-0 score in a game, I am sure that it will not be a problem for Haaland to score 20+ there neither but it all depends on the team. Put him on Chelsea and he may have hard time, put him on Liverpool and he will do it, put him on a team like City for example who lost their striker this year? He may end up scoring record breaking goals.