Yes, I don't know how people don't realize how much cheap tricks works in Chatbot Arena. A single base model produces 100s of ELO difference depending on the way it is tuned. And on most cases, instruction tuning heavily slightly even decreases reasoning ability on standard benchmark. You can see base model scores better in MMLU/ARC most of the times in huggingface leaderboard.

Even GPT-4-1106 seems to only sounds better than GPT-4-0613 and works for wider range of prompt. But in a well defined prompt and follow up questions I don't think there is an improvement in reasoning.