Why are you assuming it's the junior VFX guys making commercials? Commercials have big budgets too.
It's the same studios. They do work both for Hollywood and ad agencies.
But if ad agencies decide they're happier with lower-quality AI for 5% of the price (whereas they weren't if junior artists were still 50% of the price), while movie producers are not, then yes. They can make movies instead.
Okay, so the senior VFX artist who has the experience to get a job in the movie industry if he wants it, instead gets a job in the commercial industry because the pay is better or maybe he just prefers it, now has to work in the movie industry contrary to his preferences.
No matter which way you slice it, you're not doing anybody a favor by eliminating their job. People generally already work the best job they can manage to and by eliminating that job you're making them pick another job they otherwise wouldn't have picked, or worse and more often, leaving them without a job because they were already working in the best job they were qualified for.
The whole "now that these jobs have been eliminated, the former workers are free to find a new job!" thing is bullshit cope. Always has been. They were already free to chose another job, and chose the one you think you're 'freeing' them from. You're not giving them choice, you're taking it from them.
It's the same studios. They do work both for Hollywood and ad agencies.
But if ad agencies decide they're happier with lower-quality AI for 5% of the price (whereas they weren't if junior artists were still 50% of the price), while movie producers are not, then yes. They can make movies instead.
Does that "make sense" enough for you...?