Hi Jean-Pierre!
Lovely to chat again
I love that you're thinking this way. I totally agree on CS needing to be able to show how they drive revenue. You're only four months in so I think the reason you feel you should be tracking more is likely just the fact that the companies you've helped haven't been customers long enough to help generate new revenue.
The simplest metrics I can think of: 1. Number of reference calls provided by customers you helped onboard that were used to close deals - If you can show that by creating happy customers you are helping deals close you are impacting revenue.
2. Amount of revenue generated from expansion & upsell - Even if you throw these deals back to Sales you were still the opportunity creator and so should track the Jean-Pierre Qualified Lead (JPQL)3. Renewal rate - Do the customers you onboard renew at a better rate?
4. Time to expansion/upsell - Do the customers you onboard buy more earlier than others?
What else have you been thinking?