Most of their revenue would be from corporate contracts. An infinitesimal portion of their revenue base is interested in this.

Are you basing this on how you feel about Proton or actually have some reference/data to back it up? Proton is a heavily individual user subscription based company, calling business contracts most part of their revenue probably misses the mark by a large margin. The fact that they do PR and damage control on reddit all the time and pretend to care about public criticism just validates this more.

To continue this more it seems Proton has about 50000 firms registered to its domain

https://technologychecker.io/technology/proton-mail

most of which seem like small business with less than 100 employees

https://www.appsruntheworld.com/customers-database/products/view/protonmail

where on individual level Proton has about 100mil accounts. That doesn't look minor to me.