Yeah, home internet (cable, etc) is fast. Mobile internet is not.

Seems plenty fast enough to me.

I have an old phone. I'm on one of the cheapest plans. I ran a speed test with https://speedtest.net and I got 124 megabits per second. That's 15 megabytes per second, 900 megabytes per minute, which is 90x more than YouTube's 1080p video rate of 10 megabytes per minute.

Ruffle is also available as a Firefox extension. Maybe install that and be happy: https://addons.mozilla.org/en-US/firefox/addon/ruffle_rs/