It wasn't a documented, but development intended feature.
It's been intentionally removed with a recent patch to avoid some user-side issues caused by using it.
We needed few other changes to be done before it goes live, that's why it took a place now.
We are constantly developing and improving launcher, and would like players to use it for several reasons.
Recent news, clients updates, addons management, server status, base consistency files check upon launch.
These are just a few, but we want to add way more in the future, possibly including login to character via launcher.
Regarding points, you brought:
1. Launcher is using ~80mb, it's not much nowadays (less than 1% of common user RAM, 5% of game RAM).
2/3. We added an option to disable launcher minimizing after client started, so you can start multiple clients immediately.
If you prefer it to be minimized, we added start client option directly from right mouse click on tray icon.
We aren't currently planning to change this behavior.
Thank you for your feedback.