Can you show me one instance of activist shareholders of a major company ousting a CEO via filling the board with shareholder nominated directors? And no, "imagining" it happening isn't evidence of it happening.
>Can you show me one instance
Just a quick search: Exxon directors replaced: https://www.cnn.com/2021/05/26/business/exxon-annual-meeting...
Intel CEO ousted: https://warriortradingnews.com/2021/01/14/intel-ceo-ousted-b...
Shareholder activism can work. Yes, there are plenty of search results titles that show the activism attempts to oust someone failed. However, I did not pursue further (beyond the scope of your question and lack of willing to search on your own) if the attempt still had a change towards the activist's agenda.
It seems that shareholder activists seem to be disliked in the normal business world, but the normal business world has taken us down some dark paths so I think they can take a hike. Businesses have shown they care little to nothing about the "greater good", but are only concerned about the stockholders. So people have gotten savvy to that notion, and have started to weaponize stock ownership. Just like anything else, it can used for "evil" and it was for a long time with hostile takeovers. Now, these takeovers can have an impetus for good instead of greed.