On a certain level, most people have a general idea of who they should and should not debate, with regards to any given subject with which they are familiar. This sense is, essentially, an assessment of how hard it would be to win a debate with the given person on the given subject. This assessment can be made on two different levels: how hard it would be for me personally, or how hard it would be for any given person (for a more "absolute" assessment). The latter formulation, when approached with a certain level of objectivity, allows us to evaluate - what I will term as - a person's epistemological weight class. Asking how hard it would be for us, then, is simply comparing our own epistemological weight class to someone else's.
But how useful a concept is this, really? It's awfully vague, and basically impossible to reliably quantify. However, it is something that we seem to innately know about a person, so long as we have some amount of knowledge about their amount of knowledge (or at least a means of predicting that amount). Epistemological weight class, then, is a form of meta-knowledge.
Because epistemological weight class is purely a function of the amount of knowledge an individual has about a given subject, my initial presentation of the concept - "how hard it would be to win a debate" - is actually missing a crucial addendum: the assumption of all other factors being equal. These factors can otherwise distort our initial assessment of the difficulty of victory, and are often the reason someone is able to prevail in debate against someone with a comparatively higher weight class.
So what do we do with this meta-knowledge? Here, the metaphor is fairly apt: awareness of someone's weight class allows us to better assess whether we are "out of our league". For example, I would never be so foolish as to engage Patrick Stewart in debate about the most effective methods of learning to act, nor would I dream of engaging Amal Clooney on the subject of Middle East politics. On the flip side, I would be perfectly comfortable discussing the performance and theory of vocal music with anyone below the level of, say, Diana Damrau, and Judith Butler is perhaps the only person I'd avoid if I wanted to discuss the applications of queer theory to video games, though her presumed lack of familiarity with that particular medium might theoretically give me an edge in such a debate.
We can also use this concept to leverage an idea of "epistemological weight-lifting", where one can increase one's own weight class by engaging in debate with those whose weight class is slightly higher than our own. The idea of getting better at debating by engaging in debate is nothing new, but such an idea not only fits with the metaphor, it also emphasizes the need to engage in challenging debate (which might otherwise be overlooked).
There are two further considerations needed to refine the concept of epistemological weight class: how to handle debate with individuals who cannot or do not respond, and how to handle debate against ideas (such as scientific theories or grand concepts).
Given the (fairly obvious) notion that people are able to record their thoughts and opinions in permanent exterior media separate from their own minds, it follows that it is possible to engage in somewhat one-sided debate with a person who has not directly initiated the debate, or who does not respond to arguments and rebuttals, whether due to a lack of awareness, motivation, or being alive. As they are (or, at least, were) people, they do have an epistemological weight class that can be calculated, though the accuracy of this assessment can vary wildly. However, because their arguments simply stand on their own without further elaboration or revision, they can be said to be epistemologically inert, and thus that only other people are capable of moving them through their own force of argument.
This inertia persists until the originator of the inert argument(s) re-engages in the debate, which may of course never happen if the individual in question is no longer alive. If a third individual steps in to provide "interpretation" of the inert arguments, that person is simply entering the debate and applying the force of their own weight class; their interpretation or elaboration does not change the epistemological inertia of the original arguments.
Though this assertion may appear somewhat arbitrary (and it is), intellectual concepts such as scientific theories or broad social constructs do not have an epistemological weight class. The nature of the scientific research process, as well as the myriad processes by which ideas are disseminated and accepted into public consciousness, precludes the distillation of such grand debates into two opposing groups simply combining their epistemological weight together and pushing against each other.
At a certain point, usually at some arbitrary level of widespread acceptance among relevant individuals, an idea gains some amount of epistemological independence from the individual who first proposed it. Once this occurs, debating that idea is no longer synonymous with debating the individual who originated it, and comparisons of weight class are no longer meaningful. Counterarguments offered at this stage are more akin to scaffolding meant to prop up further counterarguments, with the ultimate goal of toppling the idea through combined force of argument. Rarely are epistemologically independent ideas formulated in such a way that a single person could dismantle them single-handedly, but even more interestingly, such ideas can often be theoretically refuted by discoveries or observations from any individual regardless of weight class; thus, weight class is essentially irrelevant when engaging with them.