Why Claude Opus 4.6 works way better than Gemini 3.1 Pro High?

I wonder if it’s even 3.1 custom tools ( https://www.reddit.com/r/GeminiAI/comments/1rcplac/i_had_to_switch_to_31_pro_preview_custom_tools/ ) since I’ve had a number of baffling failures with commandline tool syntax too.