This was my gateway into the selfhosting world. I don’t think I would’ve kept going if it didn’t make such drastic difference to my browsing experience.
I think you can consider the issue solved at this point… Last thing to check is the cpu usage while the torrent is active. If it’s being pegged, that could limit your speeds.
PIA upload is definitely faster than that. It doesn’t saturate my connection but I’ve seen it upload at 5MB/s+ at times. Are you sure you have the right options for the gluetun container as shown in the wiki? You’ll see the port PIA assigns you in the logs. Testing with a linux iso probably won’t help much since the ratio of seeders/leechers is high. Try a popular newly released torrent instead.
I have the same setup but with transmission instead of qbittorrent. Make sure you map the listening port of qbittorrent to the forwarded port from pia in gluetun.
Podfetch might suit your needs.