You might be right, but I think you're being a bit too harsh.
Medvedev's break out was in the summer hardcourt season in 2019, after Wimbledon, and it hasn't been held since, yet. In 2018 he lost in 5 to higher ranked, and seeded Mannarino and in 2019 also in 5 to Goffin. Both in the 3rd round.
Tsitsipas in 2018 lost to Isner in straights, but pushed him to 2 tie breaks in the 4th round. He could have gone deep in that one. He did lose in the first round next time to Fabbiano, so still too early to tell which one was a fluke.
Zverev has a game that could translate to grass, but he a headcase either in slams or in Bo5, or both. But I think it has more to do with this than the surface.
Berrettini made it to the 4th round in 2019, where he lost to Federer in straights. Like any young player was gonna challenge Fed in 2019... still, that was also his breakout season. Had won a couple of clay titles that year, and later made the semis at the USO. With that serve and forehand could be a dark horse. He probably lacks other things, like net game and a more decent backhand; but I imagine him as a dangerous opponent this edition.
I think that Tsistipas and Medvedev will make it to the second week this year. Zverev is more of a mistery. Sometimes he seems to be getting it together, and all of the sudden he goes 5 sets against a qualifier...
Overall I think this might be the most interesting edition of Wimbledon in years for various reasons. The biggest problem with the next gen is that they seem to be waiting for the big3 to retire to start winning slams, and don't realise that won't happen until they start beating them.