Does Google penalize content written entirely by AI?

No, Google does not penalize content simply because it is AI-generated. Penalties are reserved for low-quality, unhelpful, or spammy content, regardless of whether a human or an AI tool produced it. The focus is always on user value and meeting E-E-A-T guidelines.

What is the key factor for ranking AI-assisted content highly?

The key factor is human oversight and quality control. Successful AI-assisted content must be edited, fact-checked, incorporate unique insights, and reflect real-world experience to meet Google's E-E-A-T standards and be truly helpful to users.