This is such a brain dead take. You cannot compare an OS from one developer to a device from another unspecified manufacturer with no context. No one would claim that a Samsung phone is more private than an iPhone, regardless of the "potential" in the context of degoogling, or the niche privacy switch that's present on less than 1/10,000 Android devices sold.
Yeah its much more fair to compare pixel devices to iphones. And it still matters if you install a custom rom onto it or not. In my use case yes a pixel is more secure but a lot of people who just go with the out if the box experience may be safer with apple.