Benzema is 34 years old whereas Haaland has 10-15 years of elite level within him.
Real Madrid have chased Haaland for months despite Benzema's amazing season. They'll happily get rid of Benzema to bring in Haaland asap.
I'm always hesitant over the 10-15 years stuff. It very rarely works out that way - there are basically two cases of it going that way in modern times.
Haaland has a lot going for him now and I think there's probably another level for him to go to, but to suggest he might have 15 years even of being at his current level would be incredible.
Most players only really have about 3 years at their absolute peak, and the time around that can be short, disappointing or unreliable. And we've seen plenty of cases where the peak does not line up with traditional age parameters.
I wonder how many people thought Michael Owen would be a Ballon d'Or contender for 20 years, bearing in mind how easy laughter is with hindsight.