It is absolutely absurd to say that "nothing Olynyk does on the basketball court is useful." You can argue that the sum of what he does is average or slightly below average -- I'm inclined to agree with that, in fact. But Olynyk does multiple things well, and those things have value.
First, he's a good shooting big. All of the guys you mentioned are also good shooting bigs. And those guys added three point shooting because it's a particularly valuable skill for bigs to have, and more or less a necessity in today's NBA. Olynyk didn't shoot well against the Clippers last night. But DeAndre Jordan still had to guard him 26 feet from the basket, which is where you want DeAndre Jordan. The C's offense doesn't work without bigs who can shoot. I also don't buy the idea that his three point shooting gets overrated. For instance, if Olynyk (36%) and Lopez (33%) are comparable shooters, than Olynyk and Steph Curry (39%) are comparable shooters.
Second, Olynyk is an above average defender. He's a solid team defender, positions himself well, and works hard. He's not super athletic, he's not a great rim protector, but he's an effective enough defender and the numbers bear that out.
Third, for a big he's a very good ball handler and passer. He's a solid playmaker, can get past his man on the dribble, and has really good court vision for a guy his size. For a stretch big, that's a real nice additional skill set.
As a rebounder, his overall numbers get hurt by the fact that he's never near the basket on offense. He leads the team in defensive rebound rate. He's far from elite, but is basically an average defensive rebounding center. His DRB% is 20%, which is in line with guys like Tristan Thompson and Nerlens Noel.
All in all, he's a pretty average big. He does some things well, other things poorly, and I think he's a nice enough guy to have on your team. This year's free agent class isn't going to get paid like the last one, and as an RFA I suspect he ends up somewhere near where Meyers Leonard ended up. That'd be pretty reasonable, given what he does.