It's a combination of both.
Consider Rivian which just went public at ~80B valuation (on revenue of 0, mind you). They raised ~10B dollars through investor capital and can now use that to create factories, hire employees and so on. Further, they can issue more shares down the line to finance their growth.
I agree that consumer demand is required to grow aggregate revenues/earnings, and create a stably higher economy. But in theory using investment capital to invest into productive capacity puts upwards pressure on wages, thus longer term consumption.
However, when capital is misallocated it may not result in productive growth.