In 1984 Sampson was viewed as a monster and clearly the best player of the group. He was coming off a rookie season when he went for 21/11 after an epic college career. Drexler showed some flashes his rookie year, but was a back-up playing less than half the game. Jordan was clearly thought of as well, but was far from a sure thing, which is why he went 3rd in the draft and not 1. For example, here is an article with a lot of rumored deals involving the 3rd pick for Jordan (including for players like Jack Sikma and Terry Cummings). He was not considered an all time great prospect. http://ballislife.com/terry-cummings-jordan-trade/ (notice the picture of the actual sports page at the time).
I think you are clearly looking at this through the lens of hindsight. It was not crazy at all for the Rockets to believe that a Sampson/Olajuwon twin towers lineup would destroy the league and lead to multiple titles. I mean in just 2 years together they reached the NBA Finals losing to Boston in 6 (after beating the Lakers in 5 in the WCF). The next season Sampson got hurt and was never the same. If Sampson doesn't get hurt, the Rockets could have been a dynasty. Sampson was that good and had the potential to go down as a top 5 center all time (at least in the same tier as Hakeem and Shaq behind Wilt, Kareem, and Bill).
To be honest he would've likely went #2 if any team not named the Blazers had the pick, he was viewed as a guy with perennial All-Star or even All-NBA potential. Besides San Diego offering Cummings for Jordan, Dallas offered 24 year old All-Star Mark Aguirre for Jordan (it was turned down immediately by the Bulls), while Philadelphia offered the fifth pick that became Charles Barkley + All-Star Andrew Toney to acquire Jordan (source:
http://www.chicagonow.com/medium-rare/2016/10/23-things-you-might-not-know-about-michael-jordan-and-the-1984-nba-draft/). Sure he wasn't viewed in the same light that Hakeem was, but he was viewed very highly around the league and was considered as a special prospect judging from what teams offered the Bulls to acquire his services.
This isn't looking at it in hindsight, getting a guard/wing prospect who teams were willing to give up All-Stars for (in Philly's case an All-Star
and another lottery pick in a stacked draft class!) plus another wing who has shown flashes of star potential is a really good return for a guy who you'd have some overlap with the guy you're going to select this draft (obviously Hakeem and Sampson played well together, but Hakeem was clearly the better player who would've benefited more by playing with skilled perimeter players instead of another big like Sampson - a big reason why Houston collapsed after Sampson's injury was that their backcourt was horrendous, not because Sampson was godzilla in the NBA). The Rockets would've been fine either way, but getting two guys who Hakeem can play off of in an inside-out system was the ideal move for them imo.
Side note: I simply disagree with the notion that Sampson could've been in the class of Wilt (much less Hakeem, Shaq, Kareem and Bill), the team stats don't show that he moved the needle and his individual stats (even adjusted) weren't amazing compared to the guys you've mentioned either.