You all made some really good points, and I think there's a lot of things going on in JJ's little psyche. Certainly the middle child thing could be a factor. I quoted Tim's response because I think he's got the right approach here. I think that Brad and Robbie aren't neglectful, but they are very busy. We would like to think of them in terms of the typical family, where they work 9-5 and are home every night. That's not going to be the case. They're both in high-powered and demanding jobs, and they're going to have limited time to spend, whether it's no themselves, their kids, or each other. Brad has been able to build a stronger (emphasis on the 'er') bond with Will because of their similar personality styles and because they share a passion for surfing (and men). That doesn't mean that he's neglected JJ or Darius, it just means his bond with Will is stronger.
Will wasn't calling them on being bad parents, he was pointing out to both of them that they have to step it up more on JJ's account now that Jeanine is down for a bit. I'm not sure that the meet in LA would have been vital for them to attend before, but the event in France would have been, and so is the upcoming gig in Norway.