That's the point. Organizational tanking isn't players not trying, or worse, throwing games. It's organizations purposefully not trying to put together a competitive team this year to help with two or three years down the road. The Diamondbacks weren't looking to sign any free agents to help win games last year. They benefited from creating and maintaining a bad team.
This proposal causes teams to try and win games every year. The Diamondbacks will have to jump into the free agent market and compete if they want a top pick. Under the current system they need to avoid signing anyone and keep any breakout MiLB players off the MLB roster to get that high pick.