A few days ago, I ranted about the quality issues of Gazebo’s default physics engine. There’s another problem that I consider to be very core and impactful: the latest version of Gazebo does not support the simulation of closed-chain structures. However, closed-chain structures are extremely common in real-world robot design, so the lack of support for their simulation is indeed a major drawback.
I’ve seen many people online suggest using plugins or other methods to try to work around this issue, but the absence of native support really hinders usability. In the Gazebo Classic version, simulation of closed-chain structures was actually possible, and I’m not sure if there are any significant technical challenges being faced now that have led to this change.