[...Most of these appointees do not arise from inside the respective agencies through a merit system...]
That would appear to be wildly inaccurate. Every official source says 7000 or so of the 8000 are career. They may not be ‘qualified’ in somone’s opinion, but they are career.
https://seniorexecs.org/images/documents/Fact_Sheet_-_SES_v_GS_2014.pdf
Seems to me that 7,000 appointees just in Obama years is quite a high percentage, if they were following government employees rules and coming up through the ranks. I don’t really know what to believe these days though, so thanks for the information.