It's clearly a worthwhile investment of resources to their major competitors like Mullvad and IVPN, whose Linux clients are just as good as their Windows/macOS

It's clearly a worthwhile investment of resources to their major competitors like Mullvad and IVPN, whose Linux clients are just as good as their Windows/macOS clients, if not better. In contrast, ProtonVPN's Linux app is so painfully buggy to use that you're better off just generating and using Proton Wireguard config files with command-line Wireguard instead.