It's a x1 3.0 link at 8 GT/s < 10Gbps, so yes, it's very slightly bottlenecked... (quick throughput test with an SSD, I get around 85% of the throughput I do on the native Type C ports)
... but then they're lying about the *Type C* ports on the machines with those being capable of 10Gb/s! It's the same exact controller with the same exact PCIe bottleneck.