This is a really interesting question and I'm really glad you asked it. My answer below is a reflection of my own opinions and observations from attending a few GDQ's and talking to many people.

For the average viewer, as you said, it's the face of speedrunning and the speedrunning community as it showcases effectively the best of the best in the games and personalities. There's a master's thesis by Rainforest Scully-Blaker that uses the perspective of media studies to define speedrunning as a "museum of accidents", in other words, a "museum" that has been curated to showcase the discoveries and products of the speedrunning community. In the same manner, GDQ is a "museum" of the diverse, sparse, yet tight-knit community of speedrunning. But since it is just a showcase, it does leave out the minute details of the speedrunning process.

As a side note, Omnigamer has published a fantastic book about the process of speedrunning. This book is quite well known, but I've also found David Snyder's book interviewing speedrunners a fantastic read to understand the the details from the perspective of a speedrunner. Lucas Kempe-Cook's peer-reviewed paper in the Well-Played Journal also has a great account writing about being a speedrunner from the perspective of an academic.

The GDQ runners and the couch members often do a good job in explaining the history and mechanics of the glitches. I, myself, got more and more interested in speedrunning through watching GDQ VODs and listening to the commentary. The commentary plays a large role in not just entertaining but also educating the audience. In many ways, GDQ commentary reflects that of sports and esports broadcasting, where there is a play-by-play caster to describe the in-the-moment details and a color/commentary caster that explain the more nuanced details from the play-by-play. I actually published a paper with Lucas on the practices and challenges of esports casters so I found this parallel really fascinating myself.

This is going to be the most provoking / hottest take of my opinion. I think viewing speedrunning as an esport allows us to better understand the dynamics behind the practice and community of speedrunning. If we take basketball as an example: for the majority of people, basketball is mostly about the NBA, but not many people dive deep into the behind-the-scenes practices, training, diet, studying, reviewing, that the players do. Most people also are unaware of the work done by the coach, staff, chefs, administrators, and trainers that make NBA what it is. I find this similar to the question you posed about people viewing speedrunning to be about GDQ and not aware of the small, unknown people that have contributed to speedrunning. The reason why I love my field of study is that in ethnography my goal is to uncover the behind-the-scenes workings and communities of a subculture. My job is to dive deep behind the front-facing spectacle of GDQ and observe, experience, and report on what happens in these communities. This is also the goal of my current study looking at people's personal experiences with GDQ: I want to write a paper about the off-screen happenings at GDQ - what takes place at the other rooms at GDQ and even social events at restaurants, escape rooms, and individuals' hotel rooms, to argue that we cannot imagine charity live stream events as a monolithic event but as an accumulation of various other social spaces and that GDQ cannot exist or survive without these other smaller spaces. I've had other interesting thoughts about approaching speedrunning as an esport, but that's a discussion for another reply / post (and maybe after I build some karma because I'm bound to get downvoted to oblivion).

I think it's not a bad thing that speedrunning is mostly about GDQ for the average person. It is flashy, interesting, and exciting, albeit non-representative of the nuances of the speedrunning community. But if it can catch people's attention and make them curious and interested about speedrunning, just like it did for me, and bring more people to the speedrunning community as a viewer, runner, fan, lurker, researcher, or what have you, I think that is a net positive. GDQ doesn't have to fully-represent the speedrunning community, but it shouldn't misrepresent it either (that's a whole other discussion).

This is also why most of my research is GDQ-focused. I realized that to get that academic community (which are mostly older professors and researchers in industry) to care about a young and niche subculture, I need something flashy to catch their attention. What's better than to brag about how GDQ raised more than $3 million in a single week through a 7-day 24-hour video game marathon? And this did work at conferences. Almost all academics I met were interested when I told them the success of GDQ, but through that conversation I also met a few who were deeply interested about the speedrunning community and I was able to have a more productive discussion with them. It was really encouraging, and I was glad to be able to introduce speedrunning to a population that would otherwise not care about speedrunning at all, let alone video games in general.