HST was always great in small rapid outputs of writing, which is captured well in his letters (similar to how his collection of articles are his most popular works, but these deserve a similar look).
He obviously had some sort of ADD and later on combined with a long series of drug/alcohol addictions, so it makes sense he was better in short blurbs. Even his most famous novel Fear and Loathing in Las Vegas has a feeling of multiple long spurts on a typewriter.
Which is always how he wrote. Always also at the very last minute of the magazine due date and/or because he was running out of money and needed the next advance.
I believe this is common in creative fields. Long periods of meh and spurts of greatness.
Anyway the book series is here, usually called the Gonzo Letters:
https://www.goodreads.com/series/64386-the-fear-and-loathing...
Only the 2nd one has a Wikipedia page for some reason (the 3rd one came out in 2014) but the first one (The Proud Highway: The Saga of a Desperate Southern Gentleman 1955–1967) as a young writer who is often desperate and broke was most interesting IMO, even though his life or writing wasn’t yet as it would become famous for (but definitely still as wild) https://en.wikipedia.org/wiki/Fear_and_Loathing_in_America