It's been a while since I have seen a post worth commenting on. This is definitely one of thise posts.
As a linguist, etymologist, and academic, I too come from a position of authority on this matter. While the speaker in the comic is tehnically correct, they are also using this technicality as an entry point for injecting their own political agenda.
Are dictionaries "prescriptive"? Yes, the purpose of dictionaries is to tell people what words mean so they can use the right word in the right situation to communicate clearly and effectively.
In that capacity, dictionaries are also "proscriptive", meaning they limit what words can be used in certain situations based on their type, definition, and sometimes etymological make up.
But, are dictionaries, "descriptive"? Well, before we can address that we must confront the rabid elephant in the room. And that elephant is the idea that dictiinaries are based on opinions. That is absolutely nonsense. The words in a dictionary are not, or at least were not, arbitrarily added on the whim of some "white" people (which is racist to even bring up, making this entire comic an excercise in redefing something to defend their own actions and positions, using those very actions and practices). The vast majority of words in a dictionary are made up, sure. But every word is made up, in that respect. The meanings given to them were emparted by the person or people who crafted/coined the words for the specific purpose of describing a concept in order to clearly convey that idea to others. It was for the longet time a very serious affair and people used to take great pride in making a word that described a concept accurately. If an existing word could not be used to accurately describe a similar concept, they would use etymological rukes toncreate derivative words, because that made them easier to understand when people encountere them for the first time. Dictionaries were not simply peoples opinions of what words should be in them, they were essentially linguistic ledgers.
So, where does the idea that dictionaries are "opinion", come from. It comes from the very notion that dictionaries are or should be "descriptive ". See, because words were often crafted by people to describe new concepts and ideas, there were and still are times where different or similar words with similar definitions were introduced into public use at the same time. And whether those words were recorded in a dictionary were based on things like: whether someone paid, bribed, lobbied to have them included, the creator's social/authoritative status, or how popular in use they were (public "opinion"). After all, there is no point in including a word that nobody uses in a catalogue of words to use.
So, should dictionaries be "descriptive"? They already are, technically. As I said, there is no reason to include a word that is not being used in popular dictionaries, so there are CONCISE dictionaries that contain a currated collection of the most commonly used words and their common definitions, while there still exist COMPLETE dictionaries that include all words in use and tyeir possible definitions. And that is pretty much how all dictionaries have always worked in just about every culture that was not under dictatorial or totalitarian rule.
And this is the heart of the issue. What the OP is advocating is that dictionaries and the mesnings of words should be completely arbitrarily managed. It's not that dictionaries are not objective, or at leat not that they don't strive to be, but that certain political groups would prefer to make them wholly subjective. And, if that is the case, the dictionaries would ttuly serve as in a prescriptive capacity. The words allowed to be used an their definitions would be based solely on the "public opinion" of what the words should mean, and that meaning is imparted from an authority other than the dictionary itself.
For example, the words racism & racists are currently in contention due largely in part to a political ideology attemptin to improperly redefine what racism means based on a (proper) racist framework that excludes their (proper) racist actions and beliefs from being properly identified as "racist".
If they truly believed that dictionaries were descriptive, then the entire comic falls apart because their definition of "racist" does not erase the prior understanding of "racist ", which is the argument they are referencing. Instead, their definition and all prior definition would apply because the desctionary only exists to record "describe" observed uses and not "proscribe" or "prescribe" any particular use or meaning. This would effctively render dictionaries useless as any misues or contradictory use of a word that experienced any notable trend worth recording word quickly render that word meaning less. And in the end, that is part of the plan. Once you render something like a wrod meaningless/useless, it creates a vuccum of meaning. And, at that point, an ambitious person or group can close off that vacuum by filling it with a concept of their choosing or leave it to scar over in hopes the concept will be lost forever.
Dictionaries are multifaceted. They are part descriptive, prescriptive, and proscriptive. While concise dictionaries may be compiled based on common usage via public opinion and trend, most dictionaries are an objective collection of words and their intended meanings an uses unbeholded to any authority pther than the crafter of the word and established linguistic rules of the society. A dictionary that is purely descriptive is a dictionary that is vulnerable to arbitrary, totalitarian abuse and rendered ineffective and useless.
Don't let imbeciles like the op distract you with nonsensical word salad, trying to convince you that their words have meaning while telling you that words ultimately have no meaning, else you join them in being a fool.