It is up to law enforcement to investigate all avenues in a missing persons case. Even if there were signs that Josh could have been in the water, at least talk to the people who last saw him (this did not happen). You're a smart guy Sas - I'm sure you know how crucial those first 72 hours are in a missing persons case.
The point is that SCSO had a narrative that Josh was in the water on day 1 of the investigation, and only looked into other possibilities weeks later after their original narrative started to fall apart, when in reality, that investigation should have taken place much, much sooner. This department has a history of bungling up investigations, and this is just another example of them doing so.
If you think that SCSO did everything by the book, and even the best detectives in the world would have conducted the exact same actions that SCSO did, more power to you. For me - I vastly disagree.