First, there are other apps that take the desktop Gmail experience you see in the browser and put it in a wrapper. Station is the most popular example in this class of "Electron" apps.

To quote @SwiftOnSecurity, "Electron is a cancer murdering both macOS and Windows as it proliferates. Microsoft must offer a drop-in version with native optimizations to improve performance and resource utilization...This is the end of desktop applications. There’s nowhere but JavaScript."

Electron is a resource-eating monster. Maybe, someday it won't be, but it is now.

Boxy is a native Mac app. Of all the apps running on my Mac at the moment, it's using the last memory (reported via iStat).

The experience is pretty simple. Boxy installs three apps: Gmail, Calendar, and Dashboard. I haven't used Calendar much, because I don't use Google Calendar. I use Gmail a lot though. I have several Gmail and G Suite accounts. Because I have multiple accounts, I use Dashboard.

Dashboard essentially manages all your inboxes and sends you push notification for individual accounts. When you click a push notification or select a Gmail account, Dashboard switches your mail account in the Boxy Gmail app.

The experience is totally uncluttered. Boxy is wrapper-less, meaning there's no chrome around the app window. You can also hide the side menu. It's pure Gmail or Calendar. I bought Boxy on a whim, but it's my default now. It's a double-edged sword, because I've paid more for email apps.