Docs metrics are worth so much. There's a tendency to overindex on support case deflection, which is often measuring a negative (how many support cases did we NOT get because self-service was so good). And if your docs are great, support is going to have fewer easy questions ("where do I find X? How do I get started with Y?") but more questions that require escalation earlier in their lifecycle ("I followed the great instructions but my obscure infrastructure gave me an inscrutable error message that applies only to me and no other customer").

I've often found that unsolicited customer sentiment is a hit, especially for customers won over from a competitor who either call the docs and self-service options a reason for switching or winning, or immediately call them out positively after switching.