He had to take six months off due to shoulder surgery, and has had to play a lot of minutes quickly with Horford out. It's going to take awhile to get back to full strength for him, unfortunately.
Remember how much Bradley struggled his season following shoulder surgery. It was easily the worst season of his career (not counting his rookie year). My hope is that KO picks up his play by the trade deadline.
That said, I do think KO is a 7th man on a championship contender, and not a starter. But even 7th men/ 1st big off the bench get paid a lot now, so I'm not sure what your alternative is. Ideally we will acquire that final starter via trade or free agency, and then keep Olynyk for his proper role. Letting him go means we need to acquire that starter and replace him, which we're not going to be able to do nearly as easily.