Fair enough, Nemo.
Why Alesi was hyped up as a future star in 1989-1990... I think there are two reasons.
Firstly, his overall performance wasn't analyzed properly. Yeah, he had some impressive drives, and got two podiums in 1990 in Tyrrell. But he didn't add much to this point-score in other races. So he still had some inconsistency.
Anther issue was that F1 hadn't seen a highly promising rookie for a while. Aroun 1989-1990 the top drivers on the grid had been around for a while - Senna, Prost, Mansell, Patrese, Berger all had made their debut in 1984 or earlier. So there was a vacuum in up-and-coming talent. And of course any rookie, who impressed, is immediately stunning. F1 fans didn't know of Schumacher or Hakkinen yet, who would emerge just a year later.
Some thing happened to Button in 2000. He was hyped to sky heights, because no impressive rookie had entered in 1998-99, so in this context Button looked great. If you enter after a lean period of talents entering F1, you look comparatively impressive. Because, who is supposed to take over once the current greats finish their careers? In 1990 you'd think - Prost, Mansell, Patrese, Boutsen are already all over 35 years old. They will stop soon. Who will take over? And of course your first answer based on 1990 evidence would have been Alesi, because at that MOMENT there was no-one else there!