[lookingsideways]

That was the case with the 2016 and 2017 models of 13" MBP w/touch bar - the right side had reduced PCI Express bandwidth. The 2018 model has full bandwidth on all ports.

[dawnerd]

Does the 15 have the same problem?

[SomeHacker44]

ISTR that the 15” of all generation had 4 lane TB3 ports on both sides. The distinction was the older 13” had two lanes on the right.