Both auto-forwarding and auto-reply are paid features, which makes cancelling & switching much more difficult. Gmail is a breeze comparatively. I highly recommend against using their addresses (e.g. protonmail.com, proton.me, pm.me)
Email forwarding is available for everyone with a paid Proton Mail plan.
(source)
No, Proton email addresses do not. I have ProtonMail addresses using my domain. If tomorrow I point to another email provider, Proton can do nothing about it.
Being paid feature vs free is not vendor lock-in.
You are spreading misinformation, either by misrepresenting the situation or by not understanding what “vendor” (an arguable term since apparently you are focusing on the free version) is lock-in means.