I feel like you are really underrating KO here. Why can he not be the first big off the bench? He shoots 50% from the field, 36% from the field and averages 9 and 5 in just and 2 assists in only 21 minutes. If you put him on some of these other teams and pumped his minutes up a bit they would look even better.
The thing is, Olynyk has plenty of opportunity for increased minutes and has his entire career, yet he doesn't get them. There is an obvious reason for that, in that Olynyk is who he is, which is a quality bench player and nothing more. He is basically the same player now as he was as a rookie. You know exactly what he is going to give you night in and night out, but he isn't going to give you more than that.
Some of the names you have on this list are pretty debatable. For example, Dieng averages 10 and 7 but he is also given 30 minutes a game in Minnesota's endless rebuild. Why would you say he is clearly better than KO? Also why is Plumlee clearly better? I think he has put up some nice numbers at times but he is already on his 3rd team and he may end up just being a first bench off the big like KO.
Dieng has shown a more varied overall game, is a better defender and rebounder, etc. He isn't much better than Olynyk, I just think he provides a bit more overall than Olynyk. Plumlee is a much better overall player than Olynyk. Significantly better rebounder and passer. Not an outside shooter at all, but Plumlee is pretty clearly a better overall player.
As far as your list of players that maybe would go in front of him. Some of these are downright comical. Mclemore? The Kings are letting him walk and he is considered a fringe NBA player. He was routinely racking up DNP CD on a horrible Sacramento team for a lot of the season and his numbers have declined the last 3 years. He does nothing besides shoot, and he hasn't been lights out at that even 41% overall and 35% from 3. The idea that any team would take him in the first round at all at this point is debatable.
McLemore is an odd case, I think most teams would select Olynyk, but there is something about McLemore that is appealing (he just scored 14 points in Sacto's last game and over his last 16 games is averaging over 11 a games (he has started 11 of those 16 games as well), and on the season he is shooting nearly 40% from three in just under 3 shots a game). I have no idea what is going on in Sacto, that team is a trainwreck.
Then you got Len? A guy that was also racking up DNPCD for the Suns this year and is now losing minutes to Alan Williams?
Len has started the last 8 games for the Suns. His per 36 this year are 13.7/11.6. He is two full years younger than Olynyk and has shown a natural progression. Again, depending on team need, a team could absolutely decide to take the interior player over the spot up shooter.
I can't really think many teams or anyone would prefer Snell or Delladova. Delladova parlayed a nice couple of games in the playoffs but seems like at best a backup point guard (he lost the starting job to a pretty meh rookie already). Muhammad has had the chance to prove he is a legit rotation player with Lavine, but has not lived up to the task.
Dellavedova in March has played just under 27 mpg is averaging 11.6/3.8/1.6 and shooting 50% from three on 3.5 attempts a game. He has started 49 games including the last 3. He is a better career shooter than Olynyk and is a better defender. Not hard to see a team taking the player that does the one thing Olynyk does well better than Olynyk. Snell was in the bottom category i.e. a guy that is trending in the positive direction, not a guy that would go ahead of Olynyk now. Not sure why you even mentioned him. Muhammad is similar to McLemore. Does some thing really well and shows these flashes of greatness, and other times looks totally lost.