>XP can use far more cores
Only for the 64-bit version, which was very uncommon for most of the XP lifetime.
Almost everybody on XP was using a 32-bit version, which only uses two cores at the most.
Using select 2014 PC's which are about the newest you could get that still supported XP and where proper XP drivers were easily available, a lot can still be done to make direct performance comparisons. These would be the first generation consumer/business UEFI PC's, originally shipped with 64-bit Windows 8. But also still offering drivers for W7, Vista, and XP if you were to prefer to install those instead or multiboot to them. Also among the first target machines to be expected to migrate to Windows 10 as soon as it became "the final Windows version going forward" from Windows 8.x. Some can have W11 installed without real difficulty too, and it runs the same apps correctly just like W10 without much more sluggishness.
But if you don't need more than 3.x GB of memory, and try W10 32-bit, you may find it's a lot less slow than W11. This is where nobody can deny it.
OTOH with XP 32-bit on the same hardware (including SSD and HD graphics) with all proper system drivers, nothing about it can be considered slow by comparison.
Much faster than almost all professional users of XP remember from back then, because 2014 hardware was so much more performant than 2004 or 2010.
On only two cores it just blows everything else away.
Except for Windows 98 of course on the same hardware without even proper system drivers (naturally only using a single core), but you have to remove all but 1GB of memory for that.