You're absolutely correct, though, that this is a weak QB class for the draft, which helps his stock a good bit.
Any other year, he'd probably be looking at being a priority UFA.
He's a very good athlete, and has the leadership qualities, but the pros want to see someone who has the ability to throw the ball with consistency and accuracy when it comes to the intermediate and long routes.
He'd be a longer term project, and not someone who could help out at QB right away, unless there were some horrible disaster with the QB depth chart.
Sometimes, a quarterback is an absolutely outstanding athlete, that a team will take their chances on him early on, hoping that all he needed was better QB coaching.
As good of an athlete as Leonard is, though, that's not going to be enough to warrant an early draft pick on him. The kind of QB who has the athleticism I'm thinking of would resemble someone like Michael Vick or Anthony Richardson (eye popping athleticism).
To put it this way, the other "wild card" quarterback in this draft would be Jalen Milroe, and he's looking at being around a 3rd round pick, even with his being the best long ball thrower in the class.