> 2000Mb / (3600s * 2) = 277.8Mb/s

2000Mb / 7200s = 0.278 Mb/s, or 277.8Kb/s

> It is very spiky, but frequently jumped between 150kbps and 200Mbps. […] I think it’d get bogged down with 4 people

That’s just burst buffering as fast as it can, you didn’t capture the average. It doesn’t suggest it would slow down with 4 people. 4K on YouTube takes 20Mbps, so to parent’s point, you’ll have plenty of bandwidth to spare if 4 people do this at the same time on a 300Mbps line.