Zoom seems to be optimizing for bandwidth use, and by extension, cost to them. Its typical use case is a shared office internet connection.

Discord users are more likely to have a dedicated fast internet connection and doesn't seem to care about profitability at the moment.

It's just the difference in designing for a 100/10 connection to yourself vs sharing a 100/100 connection with 20 other people. Zoom reasonably gracefully degrades on choppy/slow connections while Discord becomes straight up unusable.

Ah, this makes sense. I have noticed that Zoom never quite gives up for participants on slow / bursty networks. When something becomes that bad I expect it to be headed towards failure, but Zoom is happy to just sit there at 0.5fps.