> Blocking email or gmail is much closer to a nationwide internet blackout than blocking signal or tor.

Yes; the point was not that they’re the same, but that regimes that do the former tend to also do the latter. Moreover, we shouldn’t do insecure things because regimes block the secure things; that’s what the regime wants you to do. The answer might not be Signal if Signal is insufficiently decentralized, but it certainly isn’t email.

> for most nations, an active connection to imap.gmail.com leaks little other than how actively the user uses gmail

This alone is a significantly larger amount of metadata than schemes like Signal leak. But it also isn’t true: a country that controls its internet infrastructure can almost certainly pull much more metadata from plaintext IMAP/SMTP than just access times and addresses. And this isn’t hypothetical: STS is not widely adopted in the email ecosystem, so plaintext downgrades are pervasive.