He is often running two or three streams. You may not hear him come back to you if you can only copy one of them.
Hmmmmm. why would it be that if you can copy 1 stream you can't copy all of them? Now I know it happens sometimes, BUT usually if you can copy one stream you can copy the others. The power of the station (lets say 100 watts) is evenly divided among the number of streams. So USUALLY if you copy any of them you copy them all.
Of course one stream could be overrun with a lid transmitting on it, or there can be propagations reasons one may not make it to you. But USUALLY you will copy all of them. After all they all originate from the same transmitter at the same time.
Just like a SSB signal will have audio from say 300 Hz to maybe 2800 Hz. and I suppose there could be some degradation of some of the audio information in that bandwidth that might make copy a bit rough, but an FT8 signal of a station that is running 3 streams and the lowest is on lets say 310 Hz and it will be 50 Hz wide so to 360 and the next stream will start on 370 and run to 420 and the next will be 430 and run to 480, that is a pretty narrow band of frequencies to lose a significant amount of information due to propagation anomalies.
As for the QRP er as noted above, I guess he calls on SSB without ever hearing the DX too? After all it makes perfect sense that if he never hears your callsign calling, he will never acknowledge you either. But how would you know if he acknowledged you or not? Are you to just assume he will put you in the log if you never respond to him? The man is a believer in fairy tales.
It saddens and disappoints me that such a large percentage of the ham population is so obtuse and uneducated, but I am finding out it is the truth, and has always been so.