My main issue is that you can't access the dashboard from the multiplayer page anymore. I mean: Having it on the main page under a fall down menu is nice and all, but it increases the amount clicks by 2.
I think you mean by 1? It's two clicks now: MultiPlayer, then Dashboard. It wasn't 0 clicks before, unless your computer could read your thoughts :)
Really the trouble with the old sub-tab system was it wasn't mobile-friendly. The links were super small, and there's no way to fit that many links in on a small device without taking up too much space to be problematic. Mobile-unfriendly sites also gave us a ranking hit on Google, so it was a big problem. So the site uses bootstrap now, which uses these drop-downs.
As a work-around you could always add the page to your bookmark bar on your browser you can just click it there.
My 2nd, minor issue is the 2nd page that opens up when clicking play. The 2nd page is non-tabbable which I find annoying
The reason for the new window is a technical one: If there are HTML elements on the same page as the webgl app, they can get focus and the any keystrokes like "enter" activate them and navigate the page away when the player didn't want it to. It's a side effect of the fact that browsers don't put focus onto the webgl elements properly.
The app actually originally launched the Unity app in the same window, in the same window underneath the top tabs, and it was an endless source of complaints and frustration from the community. People kept navigating away when they didn't intend to, so it was a big problem. Once it was changed to a new window without html elements, it solved the problem.
Another issue was the back button -- players would often hit the back button, either accidentally or because they were trying to go back within the webgl app. Both of these would close the app, and since it takes so long to load it was very frustrating. Opening in a new window ensures back doesn't close the app.
As a workaround you can always middle-click the link which will open it in a new tab instead of a new window, or add https://www.warzone.com/Play
to your bookmark bar and use that instead. That will open it in the same window, just be careful not to go back.