I really don't think that's true outside of the HN echo chamber. Like OP, I am using a Macbook Air which is hardly a supercomputer and vscode runs perfectly fine on it.
"I raise elephants, but they are bred to be as small as possible."
"They're _either_ elephants, _or_ bred to be as small as possible."
Why do we have to make this complicated? The creator is using Electron, and within that given framework putting focus on RAM optimization. Moving on.
Emails have become much more than that. They can contain almost everything a webpage can.
Most browsers use a ton more ram than 300 MB.
In absolute terms it may be big. But for an electron app it’s probably not too bad.
If you mean this, it's written in Swift https://macos.telegram.org/
What OS are you using Telegram in?