There are even now niches in gaming that are under served, and games in these niches are much easier to market.

You can engineer a relatively high chance of success but it requires two things:

1) Actually picking an under served market. Meteriodvania style games are not one of these, there are a ton of game out there fulfilling that need.

2) Really really understanding the audience. You have to know what details of the previous games in the genre were actually important, and what were not which you can innovate in. Even the tiniest details can be super important.

It is obvious what finding a market in indie games means and that you can't imagine it shows that you aren't particularly creative. There are a couple of different approaches to finding a market. Find a game that is fun or popular but doesn't have a polished or commercial version and make that. Find a set of users that would like to play games but doesn't have many games that appeal directly to them and make a product for them. Find an old game or genre that hasn't had a release and make a game in that style. Release a lot of small experiments and prototypes, build a small audience around one of them and iterate, killing ones that don't catch on, etc. Finding product market fit with and indie game might not always be cheap or easy, but there are a variety of ways to do it and it's definitely not unimaginable.