He showed me his WhatsApp: People are sending _ALL_ type of critical documents by WhatsApp to him. Everything. (and bank statements are among the class of "less critical" documents in his case)
My theory here is: "If you have any function in your product, people will use it for anything appropriate to them in a given minute"
Sending it via WhatsApp (which also has desktop clients, btw) strikes me as a perfectly reasonable solution. (Which is somewhat of an indictment of the current state of cryptographic software, but that's a different topic.)