And there are also a lot of people who said Kobe and Lebron would be all-time greats after seeing them play as rookies... and they're maybe not so far off there. Just saying.
Kobe looked awful his first season. He was drafted 16th (I think). I don't think anyone was calling him a future all-time great.But, I do get your point and will note it is valid. Just as many fans were claiming Damon Staudamire, Tyreke Evans, Elton Brand, and plenty of other players with good rookie seasons, were going to be great.
If we want to use basketball, plenty were claiming
Tyreke Evans and Brandon Jennings were going to be special after great rookie seasons. Not even a year later and they came tumbling back down to earth, due to no fault of their own. Their games were NBAready, but that doesn't always translate to elite careers. If fact, in rarely ever does.
If you want to use football, Ryan and Flacco are two great examples of this happening. Ryan was a flashy top 5 dynasty QB not too long ago.