True, wouldn't be too different vs just using a VPN. You're choosing to trust the Tribler tech and the Tribler exit node operator vs choosing to trust the VPN provider. Granted most VPN connections are going to have much better performance vs anything Tribler related.
There is a nice side effect of running an *arr stack against Tribler, even in 1 hop mode - Your Tribler node is much more easily pulling in new content into the Tribler network for other users to access afterwards without needing an exit node. Ideally it's just one Tribler node/user needing to pull data through the exit nodes while the rest would just pull it from you and share with other nodes in-network.
Torrents over I2P work the same way. If the torrent data isn't found within I2P and you have outproxies configured you could pull torrents from the clearnet & afterwards other I2P users just share amongst the I2P network.
If the VPN provider does not support port forwarding then it is normal and expected to always be firewalled. Toggling random ports doesn't change that fact.
Not sure why you would sometimes see your status as fully connectable, guessing either it's a Windscribe misconfiguration when you initially connect (?) or qBittorrent gets confused during the intitial connect. Or there's some other misconfiguration.
You might want to see if other people using that VPN provider have more insight, maybe they are doing something strange with the ports when you initially connect & eventually close them on you.