"The king of weapons is a blade" is the most stupid assumption I've ever heard.
The only reason why the sword was ever invented is because it is the most effective weapon to kill other human beings, before the invention on explosives and biological/chemical weaponry.
The king of weapons obviously has to be a blunt weapon, simply because it can damage even the toughest monster with scales/exoskeletons. A blade can never do that. It will either get chipped or deflected or reflected when hitting against a hard surface.
The blunt weapon can either cause fractures to the armor of the enemy or hemorrhage/fractures to the tissue below it.
Especially with the enhancement of human strength to a level far beyond the normal limits, a very heavy club/mace/hammer/pick will enable you to deal with every enemy that isn't too small & fast to hit (in which cases the sword also fails spectacularly).
The reasoning that a sword is strong thus is but an homage to Dragon Quest/Final Fantasy/Seiken Densetsu and other classic JRPG franchises, but not really applicable in an isekai setting that is based on the laws of our universe.