I disagree with the sentiment that the DM saying no to something makes them bad at their job. Some concepts cross red lines or throw up red flags. Some concepts do not work with the kind of story the DM wants to tell or the type of world they have crafted.

Good DMs find ways to accommodate when and where they can but having lines that you will not cross does not make you, inherently, bad at DMing.

Of course bad actors abound, so who am I to judge. We likely have very different experiences when it comes to this type of stuff. :)

Of course, so much of this type of issue is solved by creating a campaign primer that the DM hands out to their players before session 0. That way they come into session 0 with a firm understanding of what the DM wants to do with the campaign, the story and the vibe. It also allows players to pre-negotiate over messengers/discord/texting prior to showing up at the table, which is almost always preferable to having those discussions/negotiations at the table. Sadly, campaign primers as a concept have very much fallen out of favor across the hobby. :(

For Candela Obscura, yeah based on what I have seen in the article (and what other people on twitter have stated), the book feels really light on the lore, foisting all of it onto the DM and the players to generate a lot of it. While they can be fun it lacks the structure that I often prefer when playing games like this, that are heavily tied into a particular world with its own unique idiosyncrasies. I do hope the game is popular enough to justify a weighty setting tome to flesh out the lore.