I'm not sure what is unclear. From your own reference:
Throughput: The number of work items “finished” per unit of time.
So if you get asked: "How many units do you finish in an amount of time", this would be the obvious metric to make predictions. "We finish 5 units per day on average, so we should be able to finish around 30 by Friday next week".
Both of the metrics that you cite (along with a probability) answer the question "When will this piece of work be done?" When your stakeholders ask that question, you have an answer to give them based on your data.
Don't think of it as providing metrics to stakeholders. In my experiences, they don't care about metrics. They care about how long it will take ...
There is no one right way to develop software, so I can't say that what you are doing is wrong or right, but I don't think you can compare it to CD or Kanban best practices because you don't seem to really be doing either.
Continuous Delivery is exactly that: continuous. There are no release batches in continuous delivery. Now, it is fair to say that ...