I highly doubt that’s what’s being said.
More is expected of students in senior seminars than is expected of freshmen in first year writing seminars, just as I’d think seniors studying history in a 300 or 400-level course are expected to be able to produce work that is different than freshmen in their first college 100-level history course.
Suggesting anything else is like saying freshman students who do well in first semester Gen Chem should get Fs but seniors in advanced chem courses should get As, no?
Most humanities profs provide some sort of rubric or guidance as to what is expected for major assignments or exams. My own profs, and my Ds, both accepted early work and gave feedback as to how to improve too, either before the grade was assigned or after. Maybe that’s only possible at LACs with small classes, I don’t know.