Who will be 'better' is hard to say because what defines 'better'? To one, better is what shows up on the scoresheet. For another, better is about much more than just points.
(eg: I'll use the Canucks as an example. Is Bo Horvat 'better' than Brock Boeser?
Boeser puts up more points, but I'd take Horvat over Boeser as the better player because he does so much more that doesn't show up as goals & assists and brings more to the team IMO. But not all may agree).
If it's purely goals/assists, then Kakko will be 'better'. I'd wager he ends up the better scorer over his career than Podkolzin.
But Podkolzin could very likely end up the better overall player if you believe that things like defensive game, hits, sticking up for teammates, killing penalties, leadership ability etc. are just as important.
In a nutshell - IMO, Kakko will score more. Podkolzin will be the more well-rounded overall player.
Both NYR and VAN are lucky to have them and I'd doubt fans of either team would trade one for the other.