Yes, this time span held true for my stepFIL, although I would say he didn't have good care at the beginning and became a ward of the county later and I'm not sure of the quality of care he received after a certain point. I think those who have the financial means and access to really great and frequent medical care may have a "better" and longer journey.
Read more here
https://www.agingcare.com/articles/facts-about-lewy-body-dementia-174545.htm