I think a lot of folks here are suffering from flash PTSD from the early 2000's. I remember those days. I remember when a flash intro was blocking and cumbersome and slow. But I don't feel these animations are giving off the same vibe because:

1. They are non-blocking of both the loading phase and the content area. You can scroll right past them if you don't want to look because they are inline content elements. They are essentially "animated heros".

2. They load fast, actually less then the total size of some full screen hero images because it's a WebGL scene.

3. They are short and quaint - you might spend the same amount of time observing some small details in a hero image or banner.

4. They downscale to mobile without a quality loss.

I think like any other element in design, it's how it's executed... If back in the early 2000's flash was integrated in a less obtrusive way it might have been a better experience.