People started reading the series now?
The Shichibukai couldn't be arrested or hunted by the Navy, therefore they could unleash levels of terror to civilians without repercussions and can only be forced out after defeat (from an other force that it's not the marines, in this case: SH's).
Fuji Abolishing the Shichi, made that impossible for them, they can now get hunted and can't indulge on they terrorism acts without having an Admiral on their trail.
So another Dressrosa or Alabasta incident will not happen, and that was Fuji's purpose, them joining and becoming a Yonko Crew does not make his decision wrong, simple because they are also unreliable to the Navy.
-Kuma sent the SH's away.
-Hancock attacked both forces on the War.
-Mihawk bailed when Shanks came in.
-Doffy did what he wanted only.
With the SSG, whatever it is, that won't happen anymore, especially something hand created by Vegapunk.