I assume these wounds described of a 1689 battle were from Scottish claymores:
"Many of General Mackay's officers and soldiers were cut down through the skull and neck to the very breasts; others had skulls cut off above their ears like night caps; some soldiers had both their bodies and cross-belts cut through at one blow; pikes and small swords were cut like willows..."
But were those through steel helmets? I really doubt that! I'd first believe there's a little hyperbole here. Also, cutting pikes is quite a different matter than cutting many other kinds of spear. Pikes were extraordinarily long, thus harder to move out of the way. Spear shafts can be cut, if they are anchored, but are much harder to cut if held in the hands. Pikes were sometimes used butted against the ground and the foot of the pikeman.
Skallagrim did a recent video which shows that a held (not anchored) spear shaft is pretty hard to cut in one blow. However, it's quite possible to destroy a spear if 3 or more cuts are placed in close proximity, even when the spear is held in the hands. I would guess that's what the author is talking about.
"Many of General Mackay's officers and soldiers were cut down through the skull and neck to the very breasts; others had skulls cut off above their ears like night caps; some soldiers had both their bodies and cross-belts cut through at one blow; pikes and small swords were cut like willows..."
https://books.google.com/books?id=lFwJAAAAIAAJ&pg=PA32#v=one...