GSP was the new breed of well-rounded fighters. Billed as the next champ. Then-champ Hughes saw him as the future of WW as well, even after beating him. The UFC loved GSP when he was young. Also got Canada behind him. So yes, top prospect.
Anderson was seen as a good striker, but was behind Shogun as a prospect, even though Shogun is younger. Behind Ninja as well. Spider's a late bloomer. He became what he was when Nog took him under his wing, left Chute Boxe. Nog eventually gave him his black belt. Started peaking in Cage Rage. Had some badass fights there against Rivera, Murray and the Fryklund elbow. Wasn't a top prospect when young, but very underrated when he started priming...which Leben and others found out.
Jones got a lot of steam with the Gusmao win, and double that when he tossed Bonnar around. Trained out of his garage back then, so the narrative was getting all his talent to a top camp and watch him eventually become champ. He got the shot against Shogun as a replacement earlier than what was thought to be his path to the title. So his prospect status didn't last long, but it was there, pretty much unanimously.
I don't recall hearing anything of Fedor before he started beating up everyone in Pride. So I'm not sure with him.