User reports Claude outperforms GPT-4o on deep document analysis: catches logical contradictions, rewrites tone accurately

A long-time ChatGPT Plus user recently shared on r/ClaudeAI a detailed comparison after hitting a wall with GPT-4o on a document analysis task. The work involved parsing a ~15k-word technical document, identifying logical inconsistencies, and rewriting sections while preserving a specific tone and structure.

Key differences observed

• Depth of analysis: Claude 3.5 Sonnet caught three logical contradictions the author had missed — subtle timeline conflicts and a statistical claim contradicting an earlier framework. GPT-4o provided surface-level summaries and lost context after a few exchanges.
• Rewriting quality: When asked to rewrite inconsistent sections, Claude restructured the flow to resolve contradictions naturally without band-aid fixes. GPT-4o kept reverting to a generic professional tone despite prompt adjustments.
• Tone matching: Claude matched the author's actual voice, not a polished corporate version, after a single instruction.

The author used GPT-4o and Claude 3.5 Sonnet for the comparison, and noted they still use GPT for quick tasks, coding help, and brainstorming, but for deep engagement and quality writing they now start with Claude.