I've been a subscriber for 5+ years and have zero issue with the loss of port forwarding. I use my devices for everything from gaming to torrenting, and haven't run into something cause a problem that required me to use port forwarding on mullvad.
what has been an incredible source of frustration as a user of Mullvad tho is when websites block me or hit me with repeating captchas. I've also had a huge uptick of spam coming in from weird domains. Obviously not sure if thats mullvad-related, but sounds like the issue of "individuals have frequently used this feature to host undesirable content and malicious services from ports that are forwarded from our VPN servers".
The removal of this feature seems to be a better of two difficult options.