I would say their vision has been mostly successfully realized, in that it was meant to be a slow rebuild, and if it is slower than expected (which it will be if they don't make the playoffs this year) that is based on the fact that what they inherited was even worse than they thought it was four years ago. Klentak's failure in the big picture has been sticking with those guys too long. It now looks like 5 of last year's starting 8, all Amaro-acquired players (Crawford, Alfaro, Williams, Franco, Herrera) need to be gone (and three of them already are obviously). And the same thing has happened with the rotation (including most of the AAA guys). Of the non-FAs, only Velasquez and De Los Santos are Klentak acquisitions.
To fill those holes you either have to extend the rebuild until better options arrive or sign/trade for risky or expensive players. He opted for the latter and maybe/probably should have finished the job with a starting pitcher, but given what has happened with Arrieta, hard to blame them for not wanting to give Corbin six years, while Happ has bombed.
Middleton clearly signed off on a vision that included, basically, doing nothing for two years. They kept Mackanin, they didn't begin the big front office overhaul until Years 2 and 3, they stuck with Almaraz and only just lost Jordan.
In hindsight it looks like it was a waste of time and money to sign the 2018 FAs (would have been better to pick third) and now the Cutch signing and Segura and Realmuto trades look shaky (though Segura has a few years left and Realmuto will probably be re-signed). But this team is hardly as bad as it looks right now. Right now it's not actually the team Klentak built. Still plenty to build around in the off-season. Right now it would not bother me at all if both Kapler and Klentak came back, I think most managers deserve three years. But if the current trend continues, even though it's mostly injuries IMO, Kapler obviously can't survive with a worse record than last season. But there's really no reason to have that conversation until it's true (or least until they aren't actually playing for the WC).