I'm a little confused by your final sentence (boom/bust prospects but without high ceilings?), but doesn't Jaden McDaniels fit here? (not all all-star, but Jazz getting killed by Jazzfanz for not taking this "obvious" pick)
Sorry if that's confusing. What I mean is that there are guys drafted later in the draft, but it's not because people think they don't have potential. There are guys who are drafted later whose potential is their main selling point. These guys are often seen as boom or bust guys. Maybe this makes it more clear with the three groups:
1. High ceiling, high floor
2. Low Ceiling, high floor
3. High ceiling, low floor (aka boom or bust)
This is obviously very generic, but I hope you get what I mean.
I actually mention Jaden McDaniels a lot when this discussion comes up. His development is a key factor in how I've formed this opinion. Jaden was considered boom or bust because he was big time recruit and bucket getter, almost like a baby Durant. Jaden still has a lot of career ahead of him, but I think it's important to note how he became a good pick. It has had almost nothing to do with his bucket getting and almost everything to do with his role player ability. In other words, the idea that people had in their heads when they thought "high potential" did not come true at all. I do not mean to say that these guys will never pan out, because obviously they do, but when they do pan out it seems like they do so by completely changing their game like McDaniels into a small usage role. And there's a reason for that, if they weren't good enough at something at the NCAA level they probably need to find another way in the NBA because it does not get easier.
If you were a bad shot creator at the college level, chances are you're not going to get on the court by doing the same thing. There are very few players in the NBA who are good at creating offense. It might be the most difficult thing to do at the NBA level and you also have to be very good at it to warrant the opportunity to do so. Even the elite prospects will usually struggle to do this early on. They are afforded that opportunity because the team has already invested so much into them, but if you're not a top draft pick they aren't going to wait for you to keep developing. I find that there are more players in group 2 that actually do become those all star, all nba level players. The main reason why is because they can actually get on the court and give themselves an opportunity to expand and elevate their game.
So when it comes to a prospect like GG, I don't automatically hate him because he was an inefficient chucker. But IMO, the conversation with him should not start with his sky high potential as a bucket getter. That is getting way to far ahead of ourselves, and I do believe you should at least be good at the thing you're getting hype for. The conversation should start with how he can help an NBA team like McDaniels did. I've said this many times before, it's not just the scoring I'm skeptical about. It's also that he was a horrid defender, passer, and was not able to use his physical tools to impact the game. He had a much better reputation for this stuff in HS, but those are still question marks.
I am open to the idea that he is better than he showed, but I am not of the opinion that we should just assume he is good at those things. If I'm going to buy into him as a player, I need to buy into a version of him we did not see in college because I can't buy into him being a better version of what we saw. This is true of most players to some extent, but the main selling point of GG has been his potential to do what he tried to do in college but better. Jaden was a 26% usage player in college with about 30% of his baskets assisted. He is now a 16% usage player who gets 75% of his baskets assisted. I don't think GG's transition has to be quite that dramatic, but going from bad college shot maker -> good nba shot maker is just not a path that works.