Kemba has not returned to full form. As another post detailed, he was actually quite good last year with many of the same players. In terms of the core rotation, Hayward and now Theis are out, Fournier and Thompson are in. He has not been that same player yet this season. Close but not quite there.
That said, I don't think having him play off the bench is the solution. If there is any change, we could have Fournier start in the Hayward role and have Smart off the bench like last season. But I don't think we are better with Kemba off the bench. All the problems will be the same. I don't see that fixing anything.
In terms of the "politics" I will call it, yes, having Kemba off the bench may hurt his perceived value around the league. That would not stop me from doing what is best for the team but in this case, I don't think it would really help the team.
I think the right thing is to keep riding Kemba as a starter. Likely look to trade him in the off season, but not necessarily. I feel if he plays out the year without injury, there will be some reasonable opportunities to trade him.
Since March 1, he is averaging 18.5 pts on 40%/36%/95% shooting with 5 assts, 1 steal, in 32 min per game. That is not terrible. If he was just a tick better in efficiency, maybe make one more shot per game, maybe a couple more FT per game, and he is right in the upper tier of PGs.
The 40% overall shooting stands out. He is not finishing at the rim like he used to. This may be fixable. Again, just make one more per game and maybe draw one more foul, and it really changes things. Then maybe make one more 3 every other game, and he is back to all star level. A lot of "ifs", I know but just trying to illustrate that it wouldn't take all that much to make a big difference.