and, even if the coders were incredibly inefficient, it probably wouldn't make much difference at all, because 4k is literally multiple orders of magnitude more

and, even if the coders were incredibly inefficient, it probably wouldn't make much difference at all, because 4k is literally multiple orders of magnitude more data than just sending coordinates of players and bullets, which even Doom was doing back in the day with reasonable (playable) latency over dial-up. As you point out, for most types of online games, most limitations are due to latency, not bandwidth.