Common practice and routine does not change the "standard" that is applied in finding cause. Just because "everyone does it" does not make it safe, legal, or mitigate a negative outcome.
The CG apparently decided that the chart trumped any unsubstantiated "local knowledge" in that case. That makes sense because if local knowledge were all that reliable the grounding would not have occurred and the question would not exist.
I think the standard is to avoid. Not avoiding can be found to be the probable cause or a contributing factor in the event of a storm related casualty.
I don't see a great deal of maneuvering room in these things, we have all gotten away with bad choices or knowingly taken risks for any number of reasons that we knew might be difficult to defend if the outcome was not what we were confident would follow. When we take a risk or an action that is contrary to defined procedures or policy and results in a negative outcome we shouldn't be surprised or dismayed when we are blamed for our acts or omissions.