I don't think it should be taken as given that there's a correlation between competency and the size of an organization that a team exists within, and I don't think such a correlation, when combined with large organizations' usage of MongoDB would challenge the assertion that there exists an anticorrelation between team competency and use of MongoDB.
Looking at the numbers, larger organizations straight-forwardly seem like they should be more likely to eventually hire mediocre talent, survive despite having done so, and more likely to have adopted any given tool.
I think you're looking at it wrong. It's not a popularity contest; I've seen billion dollar companies use fucking stupid tooling as well, but they still have the right processes where they don't lose data.
In non-tech centric large orgs, it seems you frequently do not have the talent required to be be both risk averse and productive at the same time, so "IT" becomes a risk averse and non-productive political structure from which springs an "alternative IT" rebellion group (if the initiative is lead from above) or many little cowboy teams (if the initiative is driven from below) and these will be "productive" at the expense of having no processes for avoiding stupid risks that, amongst other things, can lead to data loss.
The point? How do you draw a line from "Fortune 500s use Mongo" to "Mongo is used by competent teams"?
I specifically challenge that you can do so, given a model of a large organization as being necessarily more diverse (regressing to the mean of general competency, more likely to have facts like "org Y uses tech X" being true) and more robust to survive failures as it grows.
We don't have data, but we can still model (if nothing else, to think about what data we would need).
Looking at the numbers, larger organizations straight-forwardly seem like they should be more likely to eventually hire mediocre talent, survive despite having done so, and more likely to have adopted any given tool.