Not entirely true. The core of the engine is indeed very small but additional functionality can be added to the engine with very little effort through library projects/extensions. There are plenty of official and community created extensions in the Asset Portal.
There’s a tutorial/sample project here: GitHub - defold/sample-lights-and-shadows: Example of how to achieve pixel perfect shadows in a 2D view. There’s a few steps involved but if you start playing around with Defold for a bit its actually not hard to get it working.
Yes. Family Island is a great example: https://play.google.com/store/apps/details?id=com.MelsoftGames.FamilyIslandFarm&hl=en&gl=US
Another is Fates of Ort: Fates of Ort on Steam
Learning a game engine will definitely require that you look at documentation and/or videos. Also, there’s two different things here: 1) Learn the programming language and 2) Learn the game engine.
Unless you already know the programming language then yes, you need to learn both. This is true for Unity, Unreal, Godot, Phaser and many others. The exception is probably visual/block based engines such as Construct.
You should not worry about this. In game development/programming there’s always something to learn from a tool or language, even if you don’t end up using it. You will start to see similarities and differences between languages and tools and this will speed up the learning process each time.
There’s rarely such a thing as “click a button to make everything look good”. That is to oversimplify things. Sure, some things will be easier with some game engines than others, and with Defold you may need to a bit more work yourself to achieve certain things, while others, such as physics is dead easy even in Defold.