What's your point? People aren't required to build something equivalent before they're allowed to have critical feedback.

Isn't the parent comment complaining about the upgrade and mentions the hamburger menu as one of the "innovations"?

The hamburger menu was already there, it's not new. That's the point, I think.

Maybe they are not a Thunderbird user but I am. You can still disable the hamburger menu in the older versions. If they are removing the menu bars entirely I will stop using Thunderbird. What's the point of using a desktop app if you don't get the nice features and dense UI of the desktop apps.