I think it's relatively rare, in that most players by 22-23 are pretty much rounded and will have the technical skills they'll have for most of their career (then they'll add experience and know-how mostly), but I don't think it's that difficult in reality, but it massively depends on the player and the coach they have. Taking examples close to home for us, Rooney was a phenomenon of a player and very much geared towards the team, so he constantly added to his skillset throughout his career - Giggs was a bit of an oddity, having a longevity and understanding of his own body (and it's limitations as he got older) that enabled him to switch to something else. Rashford this year has added great heading technique to his skillset, I doubt it's a surprise it happened in the year we added competent coaching staff to the club. I think the examples are outliers, but I don't think they'd necessarily need to be, it's just that loads of players and managers are content with what they have and don't necessarily need more.Well I’m giving examples who are both from the club I support. I’m sure supporters of different clubs could come up with examples of their own. Add all those examples up…
Honestly, if Haaland carries on being the goalscorer he is, and never develops the playmaking aspect of his game, he'll still be a sensational player and one of the very best in the game.