I’d say the most trusted developer for a security oriented service is the provider, so it makes sense that proton vpn offers a proton vpn client i should say.

For the OS, i dont know it or why it needs a special version of the Linux client, and i dont really care, but the users apparently do.

As for the “22 years of oops”, if that is so why does anyone use a vpn nowadays? Security is always relative.