That was the story with CGI too, that there would be overwhelming supply that drives prices and value toward zero.
And yet Marvel exists.
Turns out in a world of infinite supply, value comes from story, character, branding, marketing and celebrity. Those factors in combination have very limited supply and people still pay up.
I don't see any reason why AI-gen video is any different.
It's still quite difficult and extremely time consuming to create a visual effect. And the technique to film actors and blend them is additionally quite difficult. If you get to the point one person can make a movie, yes you will be limited by your own creativity, but the number of people who can do that is still a lot greater than the number of people who can do that, and manage a 200 million dollar budget production and get an end product that meets their vision.