I disagree, Jackson literally has every offensive play in his game with both hands, just doesnt do any one thing exceptional.
I would also say the opposite to your general premis. The problem with the Suns roster is they have a bunch of "good adequate" guys and no real superstar potential other than Book. Guys like Warren will eventually have to move on because they were worth more minutes than they will get on Suns. This is happening with allan williams, alex len, tyson, Bknight, Ullis, and no Warren.
That doesn't make a whole lot of sense. If those players are so much better than the minutes they're getting then why aren't the Suns winning? I know we can't play everyone 25-30 minutes a night but I don't think anyone is calling for that. The players need to accept the roles they're given and it's up to Watson to make sure they're given roles that will help the team overall. There's no reason we can't use almost all of those players you listed in roles that help the team and that they're satisfied with. Not everyone can be a starter and it's not like those players could just walk onto a number of other teams to bigger roles.
Williams is an undersized but he's a good rebounder. Depending on the cost, he should return next year. Ego doesn't seem to be an issue with him so if he ends up being our 3rd string Center/3rd string PF, that's fine if the price is right.
Len has had plenty of minutes but fails to consistently produce, it's time to let him go.
Chandler is on the downside of his career, he's only good for 25 minutes a night and he's injury prone and will probably only play about 60 games. He's happy being a veteran leader though. As a veteran leader I'm sure he knows he'll need to pass the torch, unfortunately Len fumbled it every time he was given the chance to grab.
Knight sucks, he's played poorly since he's arrived in Phoenix. I know a lot of that is the injuries he's suffered plus not having a clearly defined role but he he was nothing but a chucker last year and he couldn't produce despite being given the green light when he came on the floor.
Ulis was a rookie and got big minutes in the 2nd half of the season. He will probably be our backup PG next year, which is a good thing. He's an unselfish distributor who should make his teammates better. If he plays with the 2nd unit he should give them a boost and get the most out of those guys.
Warren could be a valuable 6th man, again it depends on the price it costs to keep him long term but we have him for at least 1 more year and then he's a restricted free agent. He played that role a lot with the Suns already and produced well.