Either is better than no assistant at all. With circumstantial caveats.
If you ask the LLM to analyze those 1000000 lines 1000 at a time, 1000 times, it’ll do it, with the same diligence and attention to detail across all 1000 pages.
Ask a human to do it and their patience will be tested. Their focus will waver, they’ll grow used to patterns and miss anomalies, and they’ll probably skip chunks that look fine at first glance.
Sure the LLM won’t find big picture issues at that scale. But it’ll find plenty of code smells and minor logic errors that deserve a second look.