Has the goal post been moved enough now? The author shouldn't need to explain why a 350 MiB monster like Thunderbird isn't in their list of recommended options for making the move to basic plain-text email.
It must be difficult for you to appreciate the idea of not gatekeeping email. If you’re trying to get people to use plain text email in 2025, Thunderbird is the only obvious choice for a GUI client.
It runs everywhere and can be installed by anyone.