I don't think Olynyk is as easily gettable as people seem to think. He's not going to be bought out, he has trade value. Teams see him as a versatile veteran big that can play the 4 or 5 in different systems and stretch the floor with solid outside shooting. He's not a great defender but he's a solid one with good size. Plus, he's a good passer. He's definitely not a starter on a contending team, but can be part of a playoff rotation. I think he would cost two second-rounders at least because there just aren't a lot of big men like him around.
Also, I think some people are being way too optimistic with these minimum-salary guys we picked up this offseason. There's a reason all these guys were made available, and it'd be unrealistic to expect that suddenly in one offseason they'd improve enough be part of a playoff rotation. There's a reason Wenyen Gabriel lost his job when the Lakers picked up Hachimura and Vanderbilt. There's a reason Oshae Brissett was the odd man out in Indiana. Toronto is desperate for guards and yet they didn't keep Banton.
I think most of these signings are just flyers they took on guys (most of them are not fully guaranteed), some of which they made early in FA just to make sure they had fallback options in case they couldn't make a trade (Brissett and Banton specifically). I also think they they brought in all these guys into camp because they really wanted a competitive atmosphere instead of a situation in the past where the roster spots were more or less set. They're going to roll the ball out to Brissettt, Mykhailuk, Walsh, Banton, Stevens, and Hauser and make them compete for those backup minutes. Realistically, I can't see them holding onto so many wings (I understand Banton can also play point guard which might help him win a job).
Regarding the big man depth, I think they know they have to make a move but are going to be patient with it. You don't make a go-for-it deal like the Holiday trade and then just go into the playoffs with an old Al Horford, brittle Porzingis, and an unproven Kornet.