But if you think about it, it really doesn't make sense. Consider: the quintessence card is commonly understood to represent the overall energy of the reading, summarizing the energy of the cards in the spread. But you really can't get a proper summary by ignoring a portion of the spread (in some cases quite a substantial portion... leaving out one court card in a three-card spread would mean your quintessence ignores a full third of the spread. Seems entirely counterintuitive to consider that a summary, doesn't it?)
I understand the questions this raises given the lack of numbers on court cards, but there are various ways of assigning numbers. The best solution to that (my opinion only, of course) is to decide which method to use and then be consistent with it.
To provide a bit of a counterpoint... Thinking about it, if a quint is supposed to be a summary of the natures of all the cards on the table, it's already ignoring a huge influence - that is, the suits. Suits can of course drastically change an idea of the overall energy, like the 10 of Cups vs the 10 of Wands. If you instead view the quint as a summation of the numerical information each card has, then it makes sense in a way to leave out the courts, rather than attributing extra numbers to them that are rather tacked-on. Or, perhaps to use the 10/6/3/2 idea, which stands out as a good option to me. (Although I wonder if you'd want to use the path numbers for the majors instead, to keep the method internally consistent?)
That said, Barleywine's linked thread is a good solution if I wanted to do the former task as opposed to the latter (and would work for the latter, too), since it gives every single card a unique designation.
It's all a bit of a moot point to me - I rarely use quints, unless I'm trying out someone else's method that specifically calls for its use. I'm more of a bottom card of the deck kind of person! But definitely interesting to think about.