I agree with your last paragraph. My preference would be to put Tyreke at SG and move Thornton to the bench to a Harden type role. Obviously he can't play defense like Harden, so he'd be Harden light, but I think that would give the bench better depth. Of the three, I don't think anyone wants to win more than Cousins. And I believe in my heart of hearts, that he'll do anything asked of him, if it leads to wins. I think he's the most malleable of the three. He can be the focus of the offense, or he can be the initiator of the offense. I honestly don't think he cares, as long as the team wins.
But like all young players, if the system isn't working, or at least they percieve its not working, they then take matters into their own hands. It my personal opinion that the offense should revolve around Cousins in some fashion. He's the best player on the team with the talent to do just about anything asked on the offensive side of the ball. Tyreke is the second most talented player on the team. But Tyreke's feel for the game isn't on the same level as Cousins. If Tyreke can bring his game up a notch, there's no reason that duo can't be one of the best in the league. What I love about them together, is their contrasting styles. Once they learn how play off each other, and make those styles compliment each other, they'll be very hard to defend.
I think we agree on the "framework" of it all but disagree on the shades of it. For example, IMHO, Harden is a very unselfish player and his type of role off the bench is golden for OK.
OTOH, Thornton is alpha dog in every sense of the word. He has never met a shot he didn't like and he perceives himself as "The Man"! I can't see him buying into coming off the bench and even less into playing the type of role that Harden plays.
As others have said, Thornton is a gunner so when he comes off the bench, its instant offence. That is great but at the same time, its almost like you can't have him out there at the same time as Cousins and Tyreke because he would take away from them.
Thornton is more suited as option 1 or 2 but as you have said, Tyreke is a more talented and more "rounded" player. The only thing holding Tyreke back is a consistent jump shot. Other than the jumpshot, Tyreke is better than Thornton at any other part of the game and those are the guys you move forward with.
I also like that Cousins' and Tyreke's games are contrasting and together they could be one of the best duos in the league and it is my opinion that Tyreke being more "placid" is a great thing in this case. We all love Boogie but he is a BIG personality and an alpha dog who would do anything to win. Tyreke is more of a quiet type and would also do anything that's best of the team. Those 2 guys mesh in more ways than one. There won't be an issue of "clash of egos" between those two.
While I love players with chip on the shoulder attitude, one thing I hate in a player is selfishness or black hole tendencies and that is something that Thornton has. I am not suggesting that he is a cancer. Far from it, but his approach to this point suggest that he would be one player on our roster that would have the biggest issue taking a lesser role for the team to win. He also happens to be the least talented of the 3 players and that is not a good combination going forward.
Thornton has tremendous value as a player and as a trade chip. It is quite likely that you can get an equally talented player in return but one that is more willing to take on the role that we want Thornton to take. That is why mentioned a number of times that I would trade Thornton for Batum. I think both are good players but Batum would be more willing to accept the role or take a backward step for the good of the team than Thornton. In OK terms, when it comes to attitude, think of MT as Westbrook and Tyreke as Harder (I am talking attitude only)
And before people start saying Tyreke should be coming off the bench instead, you need to realise that Tyreke is a unique talent that brings more to the table than just scoring. He is a great rebounder for his position, a good and potentially great perimeter defender. He can create for others and himself and brings ball handing and flexibility both offensively and defensively. Tyreke is a consistent jump shot away from being unguardable where as when Thornton's shot is not falling, he becomes a liability.
And before people start talking about Manu or Harder, we are talking about teams that we built very differently to what we have.