Don't really get the Zlatan comparisons. Zlatan was most of all a technically superb forward who earned most of his plaudits for what he did besides goalscoring. He has more in common with the likes of Dalglish, Cantona and Bergkamp than he does Shearer, Vieri or Haaland.
The comparision IMHO stands on a physical parallel.
Both are very tall (6'4) and physically imposing strikers, who have a peculiar dexterity, balance, elasticity, and foot quickness that's hard to find in players their size.
Ibra wa more refined with taekwondo-honed composure and agility, and more acrobatic, Haaland looks rawer and bulkier but is still very effective with his body, and he's way faster and more explosive.
Then of course Ibra was another league with a ball at his feet, much better skills, artistry, and tight dribbling ability, but Haaland is no slouch technically in the end.
The way they interpret their role has parallels too.
They both are number 9s, no doubt abut that, but they aren't mere terminals, or target men (well Ibra obviously has become more of a static 9 at 39), they both drop deep a lot, roam wide, recover balls, challenge opponents in midfield, dribble and pass far away from the penalty box.
And they aren't just finishers - I suppose this last sentence would be taken as a given thinking of Ibra, while maybe doubted regarding Haaland, but it's interesting that overall career stats tell us Ibra as an assist every 328 minutes, and Haaland every 351 so far.