I thought it had more to do with the fact that the 3D cache is directly connected to only one of the two CCXs. Any cores on the other CCX that are in use during gaming have a latency disadvantage.

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From the Article:
Core parking is the behavior wherein half of the CPU’s cores are “parked,” or are specifically unused and avoided, when running applications that would benefit from instead running on a single CCD.
The affected AMD CPUs have two CCDs, or two chiplets in addition to the I/O die chiplet. CPUs like the 7800X3D only have a single chiplet which also has the extra cache.
With the 7950X3D (watch our review) and 7900X3D (watch our review), the reason you’d park cores is because the extra cache is on one CCD. BIOS can be set to favor the CCD with higher frequency or with more cache, but you should be using the chipset drivers for all of this. If a game is bouncing load indiscriminately between cores spread across two very different chiplets, it is possible that performance is worse. Core parking is supposed to fix this, and typically, it does a pretty good job.
If you were to force core parking on a CPU that doesn’t require it, it is very likely that you hurt the performance significantly. This could cut it by double-digit percentages. Likewise, not enabling it on CPUs that require it could hurt performance by double-digit percentages.