Although I don't have much time for pleasure reading now, I was definitely an avid reader earlier in my life, able to get engrossed in a variety of fantasy (and other genre) novels, ranging from easy to very difficult in how hard they are to read (the hardest in my experience being the Lord of the Rings trilogy, which I tackled at the age of something like 11 or 12 and was ultimately defeated by. And I was so close to the end too! But I had become completely mentally drained by it and was no longer absorbing anything on the pages. I did manage The Hobbit, though!).
A potential helper in why I read so much may be that many of the books I read were part of a series, and sometimes a pretty long series at that. So after I finished one book, there would always be the next to move on to, and when the whole series was done, I would look for the next series to get engrossed in. The popularity of Harry Potter (context: I'm British) may also have been a contributor in this regard - I haven't seen all the films, but I've read every book. As I got older, more mature fantasy novels also opened up to me as a thing that was appealing, so my options were expanded - as were what I got out of reading them.
As an aside, my favourite author is Phillip Pullman, notable for the trilogy His Dark Materials. I think he writes great stuff, although if you're going into his books, it should also be noted that he is very anti-religion, and his views extend to his writing. This isn't a sentiment I agree with; as a matter of fact, I consider myself pro-religion despite not being religious myself - yet it's in that context that I can find his work very interesting (it also helps that I just find his style of writing enjoyable - and it's not like everything he writes has to be read into at a deeper level). In his fantasy novels this is usually expressed - I won't say subtly - but unintrusively in a way that doesn't take away from the excitement of a fantasy adventure, however I have also read a short book by him that is more adult and expresses his views much more strongly - and it's the most thought-provoking thing I've ever read.
My favourite book by him, and my favourite novel in general, is La Belle Sauvage, which is the first book in a trilogy of sequels to His Dark Materials, although La Belle Sauvage specifically is a prequel. This novel works well as a standalone episode that doesn't need the following book to continue its flow, and in a nice change of pace, it doesn't even have any important themes of religion in it. Interestingly I started reading the second book in this trilogy but stopped - it feels very different in its pacing and structure, and I just can't get into it at all. So, you could say it's on the opposite end of the spectrum. I don't know if he's written the third book in this trilogy yet, if he has then maybe I ought to get back to finishing.
I would say my enjoyment of reading did and still does extend outside of books, too - when I play a videogame, I'm the sort of person who likes to read all the flavour text, no matter how pointless an endeavour it is. I will also never, ever skip through dialogue unless it's something I've read already.
Any time I get for pleasure reading nowadays, other than occasionally going towards Touhou manga and Dungeons & Dragons rulebooks, seriously those can be engrossing, usually goes towards books on Japanese legends, folk tales, mythology, etc. You can see the youkai have clearly rubbed off on me, lol. So these tend to be more like collections of short stories, although I have also recently began reading a translation of The Kojiki, Japan's oldest surviving narrative that chronicles such legends as the Japanese creation myth and the origin of the emperor's connection to Amaterasu, amongst other myths important to Shintoism, although I haven't had enough time to properly get into it yet (I literally only read the translator's preface so I've not even properly started yet, haha).
Oh, did I also mention that I studied The Odyssey for one of my GCSEs? Mythology is cool.
So, to answer your original question - doing lots of reading does, undoubtedly, improve your writing (just look at all I've written above here, lol). However I don't know if that's really the case for explaining why we don't have many essay-style videos on Touhou Project. After all, there's something - several things, actually - stopping me from producing video essays.
The fact of the matter is, getting into the video-essay making scene is just very hard. Writing about the topic is one thing, but there are several other barriers to entry - for one, you have to be very knowledgeable on what you're talking about. Then you also need to have a good environment and equipment for recording yourself speak, and then you have to actually be good at speaking when you do it, and then you need to make an actual video for people to watch, and then you need to edit your recordings into the video, and so on...
I agree, it is unfortunate we don't have more essay-like videos analysing Touhou, and perhaps also surprising given the talent we come to expect from this fandom. But it's a hard thing to make, and although Touhou does have a large fanbase it is also quite niche, so we should be glad we at least have some people who create content like this such Surnist, even if uploads are infrequent.