Anything in this article that applies to ProtonMail applies to any encrypted web based email service. There's a limit in how much you can trust ProtonMail.

If there's a website where you login and you see your email, there's always a way for that website to get access to the content of their own website.

There's no such thing as secure web-based e-mail, because web-based e-mail has the flaws outlined in the article.

Try running Thunderbird or a similar client locally, and use PGP (ugh) or something similar to encrypt messages.

(Theoretically, you can also use PGP with webmail, and it's secure, but extremely unpleasant.)

"Aside from this, I also write daily at neo-network, which is a Telegram content channel I created to spread awareness of issues on technology, privacy and security. More importantly, it shares new revolutionary technologies, and educates readers on using them to break out of the web of control, creating a neo-network in its place."

Well the author of this has a Telegram content channel.

I've been quite happy with tutanota since a couple of years.