Borgstrom is a late bloomer, that's a well-known fact. He went undrafted and then got drafted in the 1st round - that's rare. I prefer the eye test in this case - numbers don't always tell the whole story. They're a good starting point but not conclusive.
If you went with just numbers, I guess a guy like Heponiemi would have more offensive ability than Zadina.
For what it's worth, Corey Pronman at The Athletic had Borgstrom #5 in his Top 50 prospect ranking, ahead of players like Pettersson, Kaprizov, Thomas, Chytil, Makar etc.