Are you sure Lottie + SDK is heavier than the mp4? For one or two animations that hasn't been my experience, especially if you can do WebM and fall back to optimized mp4.
This was at least six years ago. At the time, yes I'm pretty sure Lottie was a lot smaller. However, iirc we largely abandoned it in favor of videos anyway because the lottie animations wouldn't render correctly without additional work.