First, I’d like to mention that the discussion about work hours is a separate discussion from the original thread topic, which was meant to focus on defining the scope of work as a core contributor. 
It might make sense to move it to a separate thread at some point, to allow to conclude the current document review.
Hours as a commitment metric?
I agree with @jill’s points, and I would even say that hours is the worst metric – but to the exclusion of every other. ;p I would love to find a better one, but that’s the only one I know that avoids having to regularly judge the relative merits of different people’s work. It’s a great equalizer – it doesn’t matter whether I think that your work was easier than the one I did, or more valuable, or more rare - these are not comparisons I would be looking forward to make regularly, personally.
If you spend 1h on any task that contributes to the project, I know that it will have been an effort in any case - that’s 1h you didn’t spend on something else! And if we agree on the scope of things that are useful or necessary to the project, then I feel that it is fair to consider it the equal of 1h of my own time, regardless of what the respective tasks were. The comparison is imperfect, but the effort look similar enough to me.
Counting hours an issue?
It’s also relevant to note that, in the interviews, most people were actually fine with the concept of counting or committing hours - the issues were more due to things like not knowing what counts or doesn’t, not knowing that hours can be a rough estimate, not being able to plan well enough, not getting enough time from their organization, etc. And often the discussion that was generated by noticing a low number of hours was very constructive, often leading to finding solutions that allowed to fix the blockers. Without the clear & simple indicator of hours tallies, I don’t think we would have had many of these discussions, as the issues would have been much harder to detect.
The goal of having a metric
It might be useful to remember that ultimately the goal is to get organizations to consistently commit resources to the maintenance of the project. Only a very small %age of the time worked on Open edX projects is contributed to the project itself – it is a long standing core issue which greatly limits the pace of the project.
Having a clear metric is meant to address that tragedy of the commons. The idea is to hold organizations accountable, by tying the ability to influence the project to the amount of resources being committed to the project itself. For better or worse, we are almost (?) all working on the project professionally - and as such, we have to prioritize contribution work in the middle of the rest of our work.
Keeping organizations accountable
Unlike a lot of open source projects, we don’t only have a personal interest in working on Open edX, but also a professional one. And it is also our professional interest to make sure the project that brings us all work keeps going and improving, and to make sure that we all chip in consistently. On the long term, this will be as important, or arguably more important, than any individual client work that we do - it’s just often less urgent, on top of the “someone else will do it” effect. To counter that tragedy of the commons, it’s important to have a mechanism that ensure that all our respective organizations properly prioritize their core contributor’s contribution work in the middle of the rest of our professional obligations, and are held as accountable to that.
In the core contributors interviews we did recently, most people usually wanted to spend more time on core contributor work, but weren’t always being provided with that time by their organization. Ensuring it is provided in a dedicated and quantified way helps securing and prioritizing that time within the context of our organizations. This is the language organizations speak. It helps us as core contributors internally in discussions about priorities, but also externally by allowing the project to escalate to organization leads when an organization doesn’t provide the time it committed for to its core contributors.
As for the volume, if 20h/month is too much @sambapete we could always find a better level - or maybe adapt it to the size of the organization/team to make it lighter on smaller ones, as has been suggested in the past? We haven’t really set a standard yet, 20h/month was an arbitrary pick. What would be the right level of effort?
Hours ranking
For ranking, it’s imho another separate topic, which is more tied to the discussion about leaderboards, etc - if we try to sort out everything at once we’ll likely not be able to decide on anything. 
But in any case, as @Dean mentioned we don’t currently have an official ranking - the report as a whole is a contributed post on the forum, and anyone is free to post their own summary of core contributor activity, as well as alternate metrics or rankings. Each would represent a unique and interesting standpoint, and I don’t think we should forbid to post certain stats or summaries. By definition, any stat will always be a simplified view of reality, but it’s a contribution and a point of view nonetheless. Other ways to present the information are welcomed, and having more diverse perspectives to compare would also allow to experiment, and help evolve them iteratively over time.
. Oh and I don’t get disparaged easily, and do totally enjoy the “democracy” of everything we do!