There are 2-3 major bottlenecks:
Extracting geometries from Revit to Dynamo is not as easy as it is from Rhino to Grasshopper. We tried to automate the process but it turned out to be much harder than what we expected with the current available public API for Autodesk Revit.
Result visualization is Dynamo is not even close to what can be done in Grasshopper. Also taking the results from Dynamo to Revit is challenging. There are a number of sample files on Hydra that shows how this can be done but I’m no expert in that area.
Dynamo is slower because Revit is slow.
Also keep in mind that the number of Ladybug Tools Dynamo plugins users are much less than the Grasshopper users. So if there are issues it usually takes longer to get a reply.
We are waiting for a project in July that might be a good chance to address all these issues and start another round of development for Revit / Dynamo. What I said above will stay correct until then.