Hubert Hurkacz needs more experience accumulated with top level players at tour level. He's still young and has a lot to learn. The good news is he's capable of more.
About Medvedev and Zverev, all I can say is that Zverev is more consistent and good on all surfaces, what I can't say about Medvedev. The Russian is like a drama queen, moody at times and not exactly great on clay as he hates it. At the moment he's better than Zverev, but not for long.