Andy Yen went on to make an explanatory statement on Reddit, which provides a few insights: https://www.reddit.com/r/ProtonMail/comments/1i2nz9v/on_politics_and_proton_a_message_from_andy/
For one thing, from the context of the original tweet – which referenced a screenshot of some other person's statement – "little guys" was quite certainly meant not as consumers but as "little tech" as opposed to "big tech". One might still consider it irresponsible and shitty to say anything good about the Grand Oligarchic Party, but what he said was not as deranged as it is often taken to be. And indeed, the Democrats do also have a long-standing problem of being in liaison with billionaire donors in particular from the tech industry (remember, Peter Thiel used to be an outsider in Silicon Valley with his pro-Trump stance); it was only rather recently that most of the billionaires decided that their interests are much better served by "Republicans".
I'm still not using Proton though. When I get around to switching to a paid provider, the top contenders right now are posteo.com or mailbox.org, but everything could change depending on what cloud plans they offer. And! it's highly plausible that we're going to see several new attractive offers being made in the next few weeks or months, so it might pay off to delay switching just a little bit.
(For calendars, by the way, teamup.com is really, really awesome. It's Swiss.)