Probably a good move as the whole Matrix ecosystem has just too many names for its own good.
Matrix should aim at becoming the email of IM and video calls, by being somewhat less obscure than XMPP. Skype and Telegram should die like Microsoft Mail and Compuserve.
If I hear the word "matrix" out of context I'm probably going to think of mathematics or material science or something else first. In other words, "matrix" is already an overloaded term, and its other meanings aren't going to go away any time soon.
It used to be there were many systems/protocols and even self-hosted in isolation email systems and bulletin boards. Some still operate to this day, though mostly delivered over the internet, but through different channels than general SMTP internet email.
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That said, email is a better term than matrix, but any other term still wouldn't be the same meaning... "matrix protocol" vs "smtp" might be more narrow/accurate.
for the end user it's just an "email client" - the problem with Matrix is that people referred to Riot as Riot being the network instead of Matrix, as Riot was the main client implementation (there are more, of course, but typically less mature).
Even the Riot app page says "Decentralised, encrypted chat & collaboration powered by [matrix]" - it's not powered by Matrix, it connects to Matrix instances. The way it's described is confusing.
I hear a lot of "my email", as in "I opened up my email" or "where's my email?" Sure they could mean their email inbox, but they also mean the email client with that phrase, and don't differentiate the two at all. Much like how a web browser is still, to many (most?) people, "the Internet" (or "my Internet", as in "I clicked on my Internet").
Both Signal and WhatsApp are much better if privacy is a priority for you.
Hacker News for example is also client to server encrypted using TLS (as are most websites) but obviously our comments are still accessible in plain text.
But to address your digression: Cloud Chats (as opposed to E2EE Secret Chats) are both encrypted in transit and at rest [1]. The difference between the MTProto implementation between Cloud Chats and Secret Chats are, at a very high level, that part of the encryption key is held by Telegram.
To be unequivocally clear, at no point are Cloud Chat messages ever stored in plaintext or sent in plaintext.
[1] https://core.telegram.org/mtproto#authorization-and-encrypti...