So Shen really is following his father footstep

Not same.

Kusho straight up expelled Zed.

Shen said nothing and left an open door behind Akali, and would always welcome her.

Kusho and Zed had chaotic break, Shen and Akali had democratic break.

Personalities also play a role. Zed was a young man power hungry and inclined to prove himself. Akali on the other hand left Kinkou Order to make Ionia a better place. Her goal is punishing the guilty. She is not tended to prove herself. She likely would sacrifice even her honor if it meant to save people.

The difference is I don't seen an outcome here where Akali kills Shen.

Well so far Akali hasn't really turned to the dark side,more to the grey side.

Well, History does repeat itself. Doesn't it?

Now I kinda want to play Zed. I hate you.

But the order of shadows is the last bastion of freedom fighters in Ionia who can at least slow down Noxus which alone is a accomplishment. They even have intel on the newest Noxian campaigns, such as artifact excavations. But anyway, the former kinkou order was harnessed by the Ionian bureaucracy that they cannot even deliver justice to a serial killer that terrorizes the whole nation for a whole decade. It was a total embarrassment. And of top of that they released said sick bastard and gave him unlimited funds and technology to be their own assassin.

Zed obviously saw the wrongs, and saw corruption within the kinkou balance. So he broke it. It is better gone and rebuilt. This is the reason why Shen and Zed are being partners now in the new lore to finish what they couldn't. Hunt down Jhin, and remodel Ionia to balance it once more.