I'm for kids being able to move if they think someplace else is better for them. Can a coach leave and immediately coach somewhere else the next year? Yes.
Coaches have to pay the buyout, grad transfers have no penalty.
Coaches rarely if ever pay the buyout (maybe Geno). The institution to which they are headed pick that up.
And at the end of the day, isn't the goal of college to graduate. Once you do, you're a free agent.