The Google Tensor SoC (built by Samsung) contains two Cortex-X1 cores - and I believe the general consensus is to only include one of these cores in a SoC due to their power requirements.
As a consequence, the Snapdragon 888 only contains a single Cortex-X1 in a three level pyramid of cores.
As I recall, the Cortex-X1 at 5nm ran pretty much neck-and-neck with Apple's A13 high performance Lightning cores at 7nm (used in the iPhone 11), with Lightning being overall a bit faster and Cortex-X1's floating point taking the lead.
I believe when Google announced they were "building their own chips" that what really meant is Google designed an NPU and seconded Samsung as their silicon proxy and told Samsung to put two Cortex-X1s in their SoC - despite any warnings Samsung may have given - in an attempt to beat Apple at their own game.
All these companies saying they're "building their own chips" despite having no expertise in silicon design are just cousin' for a bruisin' - like Microsoft using their silicon proxy Qualcomm, and ironically Qualcomm attempting the same through their silicon proxy the recently acquired Nuvia (composed of ex-Apple silicon engineers).
Qualcomm's expertise is picking standard ARM cores and putting them in a SoC with a few cache line changes - I don't recall if they've ever designed their own cores. That's why they acquired Nuvia, hoping to drain some of Apple's brain.
And so ... the Pixel 6 may simply be suffering from Google's hubris in "making their own" Tensor SoC.