Well firstly I will admit that reading it, the way it's worded is a little concerning to me. You seem to set a stage where a child was awesome, as in past tense. And then it seems you perceive that he changed dramatically nearly immediately from your explanation. Humans aren't wired like that. We do not have drastic personality shifts for no reason.
And I gather he is a handful as you say, but it's important to remain in correct thinking when something like this is going on. He is not giving anyone a hard time, he is having a hard time. Children truly do act it out when they are struggling. You will have a much easier time having no available buttons to push if you can remain in this level of thinking because you will stop taking his behavior personally (because it really isn't personal) and start to be better able to take in the big picture from an observational standpoint & start to better be able to look for where the core of this is.
Now, there are some biological things you may have forgotten, missed or maybe not realized. One notable one is that there really are 6 year molars & teething, even at this age, is an ornery business many times, much like it was at a year old. This is why I am not really convinced babies are having pain per se when teething. I have had kids old enough to talk well teeth molars & asked & they are not feeling pain according to them, yet they are ornery, not sleeping the same, not acting the same, etc. This would also explain why pain relievers were never of any help to us when babies were teething.
Now onto other things. What if anything changed after being 5? Did he start a new school? Have a change in teachers? Have a friend move away or a new student added? Has anything changed with the parents, siblings, etc?
As a very very general rule, if all other things are fine, child is developmentally fine, healthy, blah blah, a child at this age that is actively defiant has lost his desire to please you. Again, in general terms, this can come about merely from a loss of connection. If you are connected with your child, working on things that aid in bonding (such as shared activities the child enjoys, taking an interest in the things that interest them, spending time together, etc) then the child feels bonded to you. When a child is bonded to an adult, the child will naturally be inclined to want to please that adult, to gain that adult's favor, to cooperate with that adult, etc. Much like how you would feel naturally inclined to help someone you like a lot, versus someone you are annoyed with. If the child somehow feels like he is lacking that bonding with you, you can then get the opposite, which is a child that will actively seek to not be cooperative. So it's like a subconscious level of them trying to "hurt you back" because they feel hurt by the lack of connection. I do not believe, based on all I have read & what I have seen of kids this age, that they mean to do it, I think it is a normal reaction for kids at this age. This is why I asked about a change. If he is away from parents much more than he was before, if there has been a new sibling added, etc, if there have been changes that may have made him feel less loved & less appreciated, it can develop into him displaying unruly behaviors.
If that is the case, the working on rebuilding a strong connection with him would be the best way to resolve it. He would need to know that he is loved, whether he acts amazing or obnoxious, whether he is perfect, or perfectly tyrannical.
When my boys are in a rough phase, we like to watch "Where the Wild Things Are" together. If you haven't seen it, there is an opening scene that shows a boy get his feelings hurt, embarrassed, feeling rejected by his sister, etc and then he freaks out and does some pretty destructive stuff, then later he feels ignored & pushed off by his mom, etc. But the point is, he goes wild. He screams & yells & breaks things & has a mother loving breakdown. And in the end, he is sad, missing home, tired & comes back, and he is sorry.
Your son is going through a change right now. He is obviously having something happen. I also can tell you that before I had sons, I didn't know that so much emotion was involved in the ages 5-7. I just didn't know. I had no idea boys cried as much as they do either. Some of what he does that may seem exaggerated & over the top may well be quite normal. I am not suggesting that everything you stated it, just that some of it I am sure is.
And perhaps slow down a little. It sounds to me like summer hasn't had really much unscheduled time to just be. That is a very high amount of scheduled camps for a child this age. The majority of kids his age don't even do one, let alone three. I am not saying don't do them, just be sure that is really something that is working well for this child. A child can seem to enjoy something and have that be a stress all at the same time. My kids do this a lot. They love certain video games. I allow them to play until I see that the frustration & intensity of excitement has exceeded the fun factor & instead they are starting to get upset & angry. They would swear up & down the whole time that all of it was fun, that they do not need to take a break, that they are still having fun, but it is evident from watching that it's not the case & they do not have a good handle on how to set personal limits, self regulate & realize when they are just overdone. So just keep an eye & make sure that all the planned activities are helping the situation & not contributing to it.
And hopefully not, but be aware that trauma such as abuse can change personality greatly & quickly & make a child distance themselves emotionally from adults. I do not think it's likely, but it's worth mentioning.
And if you are willing to take the time to read a book, this is an excellent one for helping you develop strategies to getting back on track with connecting with him & getting a better response out of him on the things you request he do. http://www.drdansiegel.com/books/the_whole_brain_child/