It is easy to find like minded people if you look in the right places, but yes the democratisation of music has made mainstream sources useless as a cultural touchstone. For many people, none of the mainstream areas have any emotional impact, you have to dig deeper. However, even if you dig a little bit, the ocean breaks and you basically drown in a momentous sludgy breadth of continuously churned "flavour of the month" artists. What you have to do then is REALLY dig deep, again, as you say, to the artists who have no intention of actually getting more than a few hundred listens, and are fuelled only by the love of both the creation process, listening process, and dancing process.
At one point, it was pretty much just the mainstream, and there was not much possibility to really create and release music other than that.
Then, DIY movements happened, and if you scratched under the surface you found "the underground".
Now, we have layers and layers. For example, look at modern techno. Most people do not even know what techno is at all, they may even imagine something completely off-base like deadmau5 or whatever. Already, deadmau5 exists on a layer of obscurity below a lot of mainstream music. However, dig slightly further, and you reach actual modern techno, which is a HUGE industry, literally fuelling a huge part of the Berlin economy, so we have this overblown "underground" scene which is now actually really mainstream. You have to keep digging many more layers before you reach the real underground. It can take years to penetrate this...it is just so specialised, segmented, and granulated. It makes me think of Terence McKenna's weird "novelty theory" stuff: the complexity of the scenes seems to be increasing and fragmenting exponentially in and out of itself.
Thankfully, the underground is always still there, as long as someone still wants to do it.