Mr. Theodosius! In my humble opinion essay is just one topic, one question with no broken down parts so FPSC can't and shouldn't give marks distribution for that.
Secondly it is for the writer to decide what to write and what not about a specific given topic, it is part of the exam. That is what differentiate a successful candidate from the unsuccessful one.
Thirdly just have a look at outline of different essays shared at this forum in different threads and decide honestly, I don't think most of them qualify for passing marks. Same case everywhere so it doesn't surprise me atleast if most people fail this subject.
Note:
It is purely my personal opinion and
I am not an experienced person if you talk about preparation of CSS infact I haven't even started my preparation yet. So you can just ignore my opinion if you think you know better about essay writing.