I agree that we can provide much richer metrics, no argument there. I just feel that adding post count is a trivial change that provides value. That number alone can easily tell me how long a user has really been around.
These are 2 minor changes that can provide value that come at a tiny cost of 20 minutes of work. Doing all the metrics stuff is a major piece of work that is not practical before v1.
Post count is ubiquitous on all forum software, usually way more prominent than the user card. Adding it makes stuff less surprising for users that came from that world.