It doesn't replace reddit, but Discord is serving community building needs. A lot of large successful projects do support via Discords.
I know it is incredibly inefficient with the same questions being asked and answered constantly, but it appears to be what we do now. But even with that downside, it creates more intimacy/connection instead between members. So it likely leads to more engagement, even if it is inefficient.
But does that scale? It's one thing building an online community serving 100-5,000 users. It's quite a different thing to build an online community serving 100,000-10,000,000 users.
But that has not stopped some servers from exploding in size. And its "fine" if you are just trying to shoot the breeze or shout into the void, not look for specific information (which is truly horrendous) or answer FAQ (which is even more horrendous than reddit).
I know it is incredibly inefficient with the same questions being asked and answered constantly, but it appears to be what we do now. But even with that downside, it creates more intimacy/connection instead between members. So it likely leads to more engagement, even if it is inefficient.