AnotherGuy
Hero
I feel that's jumping the gun. The @Sword said the weapon of choice is unusual in the campaign world.This isn't illusionism. When the player decides their character uses a glaive and the umpire doesn't "sure check" them, they're both deciding that glaive-wielders and magical glaives are going to be a little more common in the campaign world.
By the PC selecting to use that weapon doesn't change the fact that the weapon is still unusual in the campaign world.
Same way as choosing to play a wizard doesn't somehow make wizards a little more common in any measurable sort of way or choosing to play a gnome doesn't somehow make gnome adventurers a little more common in any measurable sort of way.
Replacing magic items to suit the needs and desires of the PCs is absolutely a form of illusionism. It is the same way as ignoring the effects of a die roll, whether it be during combat or out of combat such as treasure, weather effects or wandering monsters...etc