You yourself admit he needs to be 'coached up.' Lots of quarterbacks need to be coached up, and few of them are successful.
Think about some famous examples of quarterbacks who needed a lot of work on their throwing mechanics who were drafted in the first round on their talent, and consider how they turned out. The most obvious recent guys would be Aaron Rodgers, Tim Tebow, and Blake Bortles. One's out of the NFL, one's an interception machine, and Aaron Rodgers sat behind Brett Favre for years while he fixed his throwing motion.
I think Lamar Jackson makes sense going to a team that wants to run a read option offense, or as a later round pick for a team willing to spend years developing him as a passer. In either case, if Miami spends the 11th pick in the draft (or the 43rd pick, is it?) on him, I'll blow a friggin' gasket.