That's not how image generation works. Animation and live action are not any more or less difficult than each other to a diffusion model. If anything, live action has extraordinarily more data to learn from than animation, because with animation you have different art styles with only a limited number of frames for each style (though popular and widely used styles like the standard anime look, beanmouth, rubberhose, etc. would naturally outweigh the far more niche and unique styles). Whereas there's quite literally thousands of years' worth of live action video uploaded on YouTube alone.