Well, but Executive Schedule people are essentially all political appointees, not individual contributors. This is the several hundred people who get appointed by the President- most of them requiring Senate approval- and come in to be the Deputy Assistant Secretary of Defense for Reserve Affairs or whatever. This is not the Civil Service but the political appointees who sit on top of them and cycle out regularly back to think-tanks or industry jobs when their party loses an election.
SES is not political appointees. SES are career executives, and generally serve through many administrations. Political appointees are usually 'Secretaries' and that ilk, which may be 'SES' equivalent, non-career/competitive appointments, but are not Career SES.
There are TONS of SES folks below the appointee level.
(https://www.govinfo.gov/app/details/GPO-PLUMBOOK-2020/ is the full list of these positions)