Regardless of who wrote this, I find it hard to trust an article written by a direct competitor to the company being scrutinized -- there is a clear conflict of interest here.
The adversarial system has a time and a place, but in this case it's not like Google ever publishes blog posts on why ProtonMail may or may not be bad, and it would be quite impossible for them to debunk every accusation against them.
This isn't the adversarial system as much as it is just one company making marketing material for themselves by attacking another company.