With closer integration between the application and the network layers, you can see things like the RSSI dropping (basically signal strength). This can trigger the application to start sending less data before any actual data loss happens - and the application at the local end can respond in under a millisecond rather than a whole network roundtrip.
For the traffic from the remote end, data packets can consist of "here is the low res data" and another packet for "and here is the extra data to turn the low res into higher res". The high res would be sent with QoS markers so that network hardware knows that if anything is to be dropped, drop that first. The different QoS streams could even be sent with different transmit powers and modulation schemes on the WiFi network.
RSSI goes up and down all the time for a variety of reasons. That's not really an indication of network speed though, only link speed. You can have a wifi connection over several km's if nobody else has wifi routers (in real life, they do, so you can't go much further than your house) and still have a really good link speed (from experience).
Network speed is a function of link speed AND the success of packets to reach you. When you are on wifi, your device gets a very tiny slice of time to send packets. If you have more devices, your device gets less time to send packets. Further, a "loud router" nearby (or self-interference ... or radar in 5G space -- or a microwave, or Bluetooth in 2G space) can cause a frame to be interfered with and never be received. Thus it has to be retransmitted.
RSSI is only a very small part of your overall network conditions and doesn't really tell anyone anything.
For the traffic from the remote end, data packets can consist of "here is the low res data" and another packet for "and here is the extra data to turn the low res into higher res". The high res would be sent with QoS markers so that network hardware knows that if anything is to be dropped, drop that first. The different QoS streams could even be sent with different transmit powers and modulation schemes on the WiFi network.