Or you can drag it to the launchpad...
That does nothing in my case - bug? Well it does, just not anything meaningful.
Doing what you suggested opens the app from within the dmg, rather than first making a copy to the app folder and then opening that.
While a shortcut is created in Launchpad, it points to the app within the dmg so naturally it doesn't work if the dmg isn't mounted.
(On that note, I don't think Apple have thought through how the dock and launchpad should co-exist since I'm dragging the app to the launchpad icon in the dock to be able to launch it from launchpad, the "other launcher", if I so wish. Or even more ironic: using a launcher, the dock, to launch a launcher, Launchpad.)
There's no "one true way" to install an app as there should be. Some might call that flexible, I call it unintuitive.
Until Apple comes up with something I'd rather have the blue pill back, although that was kind of a workaround as well rather than a solution.