I don't think it's a fair comparison. If WotC published a dozen new 32-page D&D books every single week, I'm sure it would drastically affect the sales figures of individual books. Comic books are just a different model.
The market is less different than you would think...
I wonder how many Marvel or DC fans there are out there?
For super hero comics, the best selling comic will sell <175,000 copies, with most being <100,000 copies. Heck, when you chart the top ten books sold each month, the bottom couple are generally close to 50,000 copies.
If there were a million comic fans regularly buying monthly books it would be a surprise.
(Based on the total number comics sold every month, if every person who bought a comic in Janurary 2020 only bought a single comic and no person bought two comics, there's be 2,775,000 comic fans.)
Okay, financials and comic industry deep dive...
As you say, because comic books are monthly rather than quarterly and there are some many, the comic industry pulls in a lot of money despite smaller sales. $361 million in 2019 compared to the $65 million of RPGs.
BUT, this gets larger when you add graphic novels to the mix, which brings in an additional $635 million. This is the big market and it's only growing: it went from $400 million in 2013 to the number above, from comparable to superhero comics to dwarfing it.
The catch is, only like $275 million of the graphic novel revenue come from comic stores. A big chunk comes from traditional book stores.
And these sales are very much like RPG books: big releases that come out two or three times a year.
And here's the side fact that most comic fans forget. That growth in graphic novels? It isn't from superhero books. It's youth orientated graphic novels.
Sales of Dav Pilkey and Raina Telgemeier dwarf sales of any superhero book, and their stuff is only released as graphic novels. The
Smile and
Dog Man series of books are the 5e of comics.