This is exactly the sort of problem that tends to go away over time (often before it becomes an actual problem for very many people). The PCI-E and even RAM bandwidth of modern chipsets would have been absolutely astounding 10 years ago.

You can share bandwidth among the ports. The default option for 8 ports would use 4 PCIe lanes for each pair of ports. But even full bandwidth for all ports is 32 lanes, not too hard to do.

How many lanes does your CPU have?

Not enough, because it's six year old tech.

But even my CPU could manage to have 8 lanes feeding a GPU and 8 lanes feeding a switch for the thunderbolt ports, something that provides enough bandwidth for the vast majority of use cases.