“those that devised the framework possessed an agile mindset” because the manifesto was written, along with 15 others, by the creators of the Scrum framework. http://agilemanifesto.org/history.html http://scrumguides.org/history.html

“Scrum fails when those in the named roles fail to live up to the role.” Don’t blame the failed results on the proven framework.

Mentioning or referencing the 100% Utilization Fallacy and “The Mythical Man-Month” would fit.

More information on why you see the collaborative roles within the self-organizing Scrum Team as an impediment to knowledge sharing would be great.