Obviously all the above could be a load of rubbish though.
Well it could be
, but I'd say it sounds like a pretty reasonable summary of the effective difference between PBN/RNAV navigation and the conventional ground navaid-based equivalent.
Those differences aren't specific to SIDs, that's just where they are more apparent.
And of course it's the ability to perform more accurate track-keeping that has been the driver for the recent trials, as previous posts have explained and with the effects on communities that have been noted.