[2020] How commercially successful is Deep Rock Galactic?

As the CEO of Ghost Ship, I can reassure you that DRG is a financial success :-) The player numbers (CCU) in August has historically been a low point and it will go up again later in the year. We are still selling well despite the time of year and I do not foresee any reason for DRG to lose momentum. After 1.0 launch, we have chosen to go for fewer (but bigger) updates and that will also create some larger waves in the curves (both up and down). The cosmetic DLCs are a way for existing fans to keep supporting the game, though selling the base game to new players is also an important revenue for us.

Rock and Stone forever!

When we ask Coffee Stain, they say we've sold 9 copies.
(Soren answers OP's question here. )

Edited for clarity.

No, it's an ongoing joke about Satisfactory only having sold 9 copies (which they have, but also a lot more).