Lucidchart is certainly more sophisticated. For example, you can easily create a floor plan (for an interior design company) simply by dragging the built-in shapes into your canva.
The available shapes are lined up on the left-hand panel. So you just choose the shape you need and drag it into the canva. That's why it is fast.
But if you are simply using the common shapes, then you can almost do the same things using Google Drawings. It is a bit slower since you need to open the 'shapes' tabs first.
But the upside is that you can make unlimited drawings, while Lucidchart only allows for 3 free diagrams.
If you have a diagram which you will be using again and again, the Lucidchart is the choice. You can insert your Lucidcharts into other Google applications like Google Slides.
Talking about Google Slides, actually, most of the things you can do with Google Drawings, can also be done inside Google Slides! The only difference is that with Google Drawings, you can create standalone diagrams. With Google Slides, your diagrams will be among the slides in a slide deck.
