Saying capital is relatively scarce compared to labor is flat out false. Look at the last 10 years or so. Venture Captial has been flush just about anywhere you look.
Capital is not money, but rather durable goods which contribute to more efficient production. It is the networks which are the capital here. Money can be used to buy capital, but only if someone goes to the trouble of designing that capital first. There is plenty of available labor looking for productive work to do, just as there are plenty of VCs searching for ventures likely enough to succeed to justify the investment. It is a lot easier to find people able to do whatever work is required than it is to find the right capital (networks) to organize them and enabled them to do the right work productively.
Both capital and labor are needed. The networks receive a greater portion of the reward because they are more scarce than labor as well as contributing more to overall productivity.
but often the network gets a disproportionaly large share of the reward (i.e., the extraction of value is higher on the network side vs the labour side). This is the same as the capital vs labour argument - one without the other isn't going to produce value, but the capital side is able to extract a higher value than the labour side.