I feel the same way personally. I feel like I see tons of people complaining about it, but it's just what I want out of a mail client. The UI is a great, the GPG integration is great with enigmail, it's a very polished product.

Not only that, but making one based on web technologies that moves away from the native look and feel it currently has would truly be a loss in my opinion. I'd probably give Claws Mail and alpine another go, maybe even desktop outlook before I'd go to something Electron-esque. I already have enough shitty electron apps - I'm currently dealing with a really weird font rendering issue arising from Electron use in VS Code.