Then his argument is even more flawed, because one can just as well pay for Gmail or Outlook and use PGP with them, without exposing himself to vulnerabilities of smaller email providers.
You are not paying for customer service, you are just becoming a paid customer[1]. And then you can compare which email provider treats its paid customers best. For me, the best treatment is when a product is so well thought-through, that I never need to contact anyone about it.
ProtonMail also offers a free inbox with a way to pay for additional storage[1]. Would you also think, that by upgrading your ProtonMail storage you are not paying for email service? The only difference is, that Gmail doesn't limit its features for the free users. It's just a different business model.