Not CS but maths
In the UK the national exam in maths taken by most school children at age 16 is called the GCSE. It is available at two levels of difficulty, foundation and higher, with a grade cap on the foundation tier. You can find examples of GCSE maths exam papers on most revision sites[1] together with the exam board marking schemes. Students take three exams each of which is marked out of 80 marks. So marking a complete set of three exam papers requires making 240 decisions. I should explain that these are written exams. With a pen. On paper. And using a ruler and pencil to draw diagrams.
The questions early in the paper are usually worth one mark each and are quick to mark - just tick or cross. In the middle of a paper you get the 'story' question type questions with several parts. So there is a non-cyclic graph with (say) three nodes and multiple possible responses to each node. Some of the 'process' marks are only available for showing correct working, some are implicit if a correct final answer is seen. Towards the end of the paper, you get a small number of 4 or 5 mark questions with much more complex 'process' requirements.
Marking a mock paper and providing decent feedback on errors and recommendations for revision for a student takes around 20 minutes on a rough average. So an hour per set per student. When I taught full-time I had between 150 and 200 students taking GCSE courses.
One parent once complained to the principal that I would not mark a complete set of past papers each week. I did mark at least two complete sets in the final term of the course and provide one2one tutorials on suggested revision strategy. I simply took the parent through the mental arithmetic above.
So yes automatic marking systems for early questions in the paper would help. I would imagine that the complexity of marking a programming task would be similar if not more complex given the number of nodes in the graph of possible solutions.
[1] https://www.mathsgenie.co.uk/papers.html is a good example. No affiliation &c See if you can write out answers to a higher tier paper in less than half an hour then scrub through the video for the full experience.