Those issues outlined with Simmons are definitely cause for concern, and it might see him slip to second or third in the Draft. I think the talent he has displayed will stop him from falling too far, if he doesn't end up being the top pick. At the same time, I think he has to be given a chance before he's written off. Some of the best players in history have been underrated and underestimated in their pre-Draft evaluations, based on incorrect assumptions or weaknesses they've ultimately been able to overcome, whether it's mental or skill related.
Maybe he is destined to be less than expected, in which case I expect there'll be a lot of people saying "told you so", because schadenfreude never goes out of style. I still say he needs to be given a chance to mature, learn, and grow as a person and a player, and an opportunity to either "get it" or not, before it's declared that he'll never "get it".
On the subject of the Boomers, though...
The concerns about Simmons' character didn't magically appear the moment he arrived on campus in Baton Rouge. Those sentiments also have been expressed by members of the Australian national team who have spent time with him at the junior and senior levels. Australian players and coaches who have been around him don't speak about him in flattering terms, calling him “the Yank” to highlight how different he is compared with most of the players from that country, and perhaps highlight how much moving to the United States at a young age and immersing himself in the AAU world has shaped him.
I feel like that should be taken with a healthy grain of salt (or unhealthy amount, as the case may be). Not to dismiss it entirely, but it also sounds like there might be a bit of sour grapes and Tall Poppy Syndrome there. In Australia, people often get overly sensitive about our cultural identity, customs, and even attitude. I mean, there are people who get really upset that Halloween has become a thing over the past few decades, because it's an "American tradition", as opposed to an Australian one. This of course is putting aside that a lot of our traditions are originally British, or in the case of Christmas trees, German. Their calling him "the Yank" could come down to a culture clash that's the result of him going through a system that's intended to cultivate professional athletes...and maybe a bit of jealousy, too.
Of course, it's not the only evidence that he's exhibited some diva-like behaviour, so again, I'm not going to dismiss it entirely. But given some of the insecurity and jealousy that permeates Aussie culture and attitudes at times, I do wonder if that part is a little overblown, and just how much stock we should place in it.