There is no need to worry. After trying a lot of engines out there, i also feel that defold is the best for 2d games among them.
Feel free to proceed, and you’ll realise that defold is easy to learn and master, and mind it, it’s really addictive. 
As for your questions,
I have never used Defold for networking, but there are a lot of solutions out there. Colyseus (pardon my spelling) for example is a very good networking solution, that allows your game to communicate with a custom built node js backend. Moreover Defold does support Playfab for networking too.
I made a game that used procedural generation an year ago, and i must admit that Defold performs awesome when it comes to procedural generation. There is also a thread here
Big tilemaps should not be a problem, as long as they are not so big that they interfere with floating point precision, which is present in every engine. But still there are ways that they can be solved too.
I remember someone asking this question some time ago. But as @britzl replied, “Defold is here to stay”. So, no need to worry, just buckle up and get started with developing some cool games. Is you ever get stuck, we are always here to help😀