I feel so disappointed when I find the Gazebo has been upgraded to such a new version, considering I used a lot of time to study Gazebo 11. Do you have a plan to migrate your system to IGN Gazebo? If you, the experts, can do it, we students may begin to migrate it on our computer.
I understand your frustration. This happens to us also.
But if you want to dedicate to program robots, this is the usual way. Things change very quickly in robotics programming and we need to adapt constantly. You need to be upgrading your knowledge all the time and many things you learnt before are no longer valid. That is the field we are in.
That is why I do not recommend to go so deep in learning all the details about a specific subject, but instead get a clear idea of how it works and where to find the specific details. By doing that, you are training your brain to change faster when changes appear in the programming language/framework/whatever.
Anyway, we are not going to change to Ignition right now because it still lacks many things. However, Ignition is installed in the base system of The Construct, so if you want, you can create a new rosject for Galactic or beyond and it will contain Ignition installed so you can launch it and practice.