Yes, very risky indeed. Particularly for a team like Miami, who need players who can make an immediate impact.
I would say "half as good" in reference to Herbert is overstating/exaggerating the impartial assessment of the two. There are those that see Herbert with a higher ceiling, but also a lower floor than Tua.
Actively planning for the aquisition of Lawrence is not an option, unless 0-16 is your plan, and we have just witnessed the flaw in that line of thinking.
Probably the only way we trade down is with a team moving up for Herbert, so it's just a question of are they willing to make it worth our while, and does the staff have confidence that Rosen can be productive enough to make it through next season?
I am really against bringing in a top FA QB. It doesn't seem like a long term solution.