Your comments

Adding this permission type would be very useful for Agency Account holders who need the owners of the websites that they manage to have permission to add their own blog articles but edit nothing else. 

This is a common requirement, as more clients want to reduce digital marketing budgets by writing and posting their own blog or news articles. To do this right now the webmaster has to give them CMS user access which also gives the client the ability to inadvertently change other website elements like H1 and H2 text tags, fonts and colours etc. This can negatively affect On-Page SEO and visual aesthetics.

Perhaps this feature could be incorporated as part of the overall overhaul of the CMS User permissions menu as opposed to a stand alone feature development.