I wouldn't agree there. One important thing that works in your favor is that there's an inverse relationship between marketing costs and market size, and a big part of that is because of a similar inverse relationship with word of mouth. Even the most fringe topic you could think of is generally going to have communities built up around it, and the more niche - the more 'airtime' ideas that cater to that community are going to get. Like in this case - his 'marketing' was a Reddit post and a Discord, for a total marketing spend of $0.

By contrast when appealing to a large market, marketing becomes a major part of breaking through simply because word of mouth is much more difficult to get going when you're vying for a market that a million other competitors, many quite competent themselves, are also vying for. To go with the games example again, if you're trying to create a platformer - you're probably going to fail, even if you create a pretty good game. It's just a completely oversaturated market, even if that market is massive. By contrast if you're making e.g. a Starflight clone - you're probably going to succeed if it's even remotely decent. It's very niche, but consequently also very underserved market with tremendous word of mouth potential.