Do cloud chatbot's system prompts make them stupider?

When I am talking with Chat GPT or Claude about abstract concepts, I am often surprised by how they seem kind of dumb... like they aren't benefitting from their extra parameters over top open models like Kimi or GLM. In fact they often seem stupider than these open models that I run locally in the way they leap to conclusions and try to oversimplify concepts and produce more "not x but y" like slopisms

My guess about why this is: system prompts are lobotomizing the model by trying to give it a "personality" that keeps users engaged. This was most egregious during the 4o era, but it feels like they still are kind of ingratiating, beyond the way pure local models usually are.

Has anyone found that the cloud models seem smarter through the raw api? Or do APIs also tack of system prompts? Or am I imagining this?