The hamburger menu is a bit lazy because there are other methods to get to the menu and most apps don't really need an overflow option set.
A good example of an app that does? Chrome, because it has 14 functions built into the one menu. For an app like Chrome where there's a ton of functionality but 99% of users need to access exactly 1% of them daily on average, this action set is unnecessary. Except when it isn't.
YouTube's overflow menu is different in that it's not really an overflow menu (though it uses the stupid hamburger, likely because it is recognizable). But accessing it is different; either tap the button or swipe right. Many apps are making the distinction to swipe for overflow options, typically on the homepage (on iOS using the swipe to go back function, on Android the left sidebar menu function). These are good uses because they are for overflow.
So what is overflow? It's all of the options/functions that an application user may need because it's important, but most of the time won't. Functions with few but vital use cases. If it's a new, small mobile app, it almost certainly doesn't need an overflow menu. If it's almost any desktop app, then there's likely one built in and spread around through the File, Edit, View, etc. menus largely built into desktop UX thanks to Microsoft and Apple.
Google isn't killing the design because Google loves functionality. Google is the everything's-still-in-beta company. So new features and functions get added, not edited out because most people don't need them like Apple does. So Google has them in apps that need them, and manages to fit in nearly every function that an app can possibly have. Hurray!