Does Olynyk have lots of potential? Not really.
Is Olynyk a player with a lot of upside? Not really
Does Olynyk play good defense? No
Is Olynyk an efficient offensive player? No
Isn't upside the same thing as potential? No, KO was not a "high potential / upside" pick. At #13 in a crappy draft, that's not a terrible thing.
That said, lacking potential or upside is not the same thing as being a finished product with no chance of developing as a player, and it seems to me like you're conflating the two.
KO is probably never going to be a defensive phenom, but there are plenty of useful players in this league who aren't great defenders. He just has to be able to fit into a defensive system. I can think of plenty of smart but athletically unremarkable (by NBA standards) players who have been able to do that.
KO is not a very efficient offensive player right now, but he's a rookie who hasn't seen consistent minutes, on a team devoid of talent. All he really needs to become a quite efficient player is for his jumpshots to start falling more consistently, and that is the sort of thing that tends to improve a lot over time, irrespective of athleticism.
It sounds to me like your expectations for the pick were unrealistic.
This wasn't a crappy draft overall. The top 10 was expected to be crappy but afterwards, it was basically a normal draft. Take this year's "loaded draft" with last year's. From the 11th selection on, Draftexpress has players like Saric, Stein, McDermott, James Young, Jerami Grant, Clint Capela, PJ Hairston etc going off the board. That's a lot of role players with ceilings mostly as solid rotation players. The quality is similar to the players who went in that range last year, like Steven Adams, Carter Williams, Nogueira, Shane Larkins, our own Olynyk, Schroeder and Giannis.
On paper, your theory sounds nice. Crappy draft, Ainge hopefully trying to salvage anything he can by getting a "safe" NBA player with at least one definite NBA skill in his shooting, which hasn't shown up yet. But in practice, it would be ludicrous for Ainge to think that because the high lottery was really substandard that he should pick differently in the mid-1st round.
Giannis can turn out to be underwhelming and certainly being skinny and tall like Randolph puts him in dangerous territory regardless of their respective skill levels and basketball IQ, but why go for the "safe" pick in the first year of a rebuilding situation. That's just stupid.