In KDE4 there was an option to add to panel by right clicking an application icon, like so
In Plasma 5 there's only an option to add to favorites
---in order to be able to make such changes!
In newer versions of Plasma 5 (like 5.12), we have two options - "Add to panel (Widget)" and "Pin to Task Manager" - when right-clicking an application icon from the Application Launcher menu:
So, there are two ways of having launchers available on the panel, in both KDE4 and Plasma5.
This can also be done by opening your application and right clicking on it in the Task Manager, then select the option "Show A Launcher When Not Running" (renamed "Pin" in later versions).
/usr/share/applications) onto the panel.
But, as I said, we do have the two options available when right-clicking an application icon in the menu, at least in the current 5.12 version of Plasma.