I'd personally say it's less that hard work is a myth and more that hard work on its own isn't enough.
Pretty much all professional comics creators I know work really hard. Most of them have, at some point, given themselves a repetitive strain injury or eye strain or some kind of stress-related illness. I don't personally know any comic creators whose comic is their primary source of income who don't work at least equivalent hours to a job that'd pay the amount their comic earns them doing some combination of creating pages, marketing, making extra materials for Patreon or organising and travelling to events in order to sell their work.
BUT It's also true though that:
- The most successful of my pro comics making friends are from a either a wealthy background or a family with experience and contacts in illustration or comics and were provided with guidance, tools, resources and contacts that gave them a huge early boost in their career.
- The ones who don't have a part time job on the side are practically all middle class and white, and most of them have a partner in a very lucrative career like software engineering or similar.
- They usually work in very popular genres like BL or they make comics that are licensed IP.
- Most pro comic artists I know who make original content have a part time job, or they make their original content passion project and also some kind of premium content for another publication that's usually in a "safer" genre or for a well known IP.
- My friends who have a strong design or marketing background or access to design and marketing expertise tend to do a lot better than people of equivalent or even superior drawing skill who don't know design or marketing.
So it's less that hard work isn't important and more that some people's hard work gets them further. That's an important distinction, because I often see people saying "I need to work smarter, not harder!" or "It's not my comic that needs work, it's just it's not being seen!" and then I look at the comic and see things like rushed lineart sloppily drawn with the line smoothing turned up too high at low resolution, very visible missed areas of colour flatting, too much text crammed into default oval tool speech bubbles and written in comic sans, frequent spelling and grammatical errors, blobby, indistinct backgrounds and other features that show that really the comic actually could use a bit more hard work before deciding that all it needs is more marketing pizazz.
So... yes, for a lot of us, hard work isn't enough, but it doesn't mean that working hard doesn't work or isn't important and the only thing a comic needs is to be a boys love or a villainess story and to get lucky regardless of quality or polish. It's more like we have to work just as hard as more privileged people but then put in more work on top of that in our marketing, or that without a financial safety net and development time to take risks with unusual genres or themes, we need to play it a lot safer with the content of our work or market ourselves to specialised niches. It's extremely rare for a comic to be successful without at least polished looking art, a clear, readable story and nicely presented text and panels whether it's in a popular genre or not.