client asked for gemini 3.5 instead of sonnet 5 for rag pipeline - any reason to push back

building a rag system for a client and they specifically requested gemini 3.5 because of the context window (they have huge internal docs). i was going to use sonnet 5 because the output quality is cleaner is there a real advantage to gemini's context size or should i push back and explain sonnet 5 is better for the actual writing part