The kick is a little unfair in the moment, because the shinobi can immediately retreat after a missed kick using the backflip, just to try it a second time. It makes a fight against Shinobi very boring, and even frustrating if you play a hero like the warden, who is very immobile.
My suggestion for this, is pretty simple. Remove the backflip after a missed attack/kick, and only allow the backflip to be used after a hit. Problem solved!
In the moment, the Shinobi is a very counterable hero, who can get punished very hard for his mistakes. His offensive playstyle can't work without a save initiator though, that's why he needs the kick. If you remove the backflip after a missed kick/attack, you will allready add a fair amount of risk to the kick, because the shinobi get's close to his enemy to land it, and in close quarters the shinobi suffers from his short block duration and low healthpool.
Without the backflip he will be forced to stand in place for atleast a short time, which will force him into a defensive position if he doesn't use attacks or guardbreaks. Attacks and guardbreaks are both counterable, and counters are a big threat for the Shinobi.

If you removed his ability to block or GB counter after his kick, you would make him to easy to counter, because of his allready weak defense and his fairly predictable attack patterns.