A bit of conspiratorial and there have already been similar threads here where some threw their suspicions against ProtonMail. I think, there are no real evidence to their claims but rather unsubstantiated. It's an interesting way to exercise one's suspicions but no need to make bold and unproved claims.Yes, there may be truth to how the internet was created and who was behind it but one shouldn't exaggerate with everything and spread unnecessary FUD. It's one thing to have those thoughts and I would rather say that we shouldn't either heavily rely on e-mail communication when there are better alternatives. Hence why Snowden have stated:

[...] Email is a fundamentally insecure protocol that, in 2019, can and should be abandoned for the purposes of any meaningful communication. Email is unsafe. [...]

(Source)