It would be handy if GC showed the data source it was using (also RWGPS and Strava).
I get a small difference between 510 and GC that I think might be due to my home being a Location with known altitude.
But BSRU I still think that you are confusing issues around accuracy of third party elevation data and the GC web site that took a ridiculous time to fix. Since this is a user forum not a Garmin support desk it'd be more useful if you provided data and analysis ahead of slagging off Garmin.
It's not fixed.