Once there was this mod: https://www.nexusmods.com/endlesslegend/mods/8?tab=description

Basically it changed unit upgrading and battles in various ways, one of which unlocked most of weapon types for most of units. Right now, as I get it, this mod doesn't work and, if there's some modders for this game that's still alive out there, I would love to see someone make a similar mod or somehow update this one so it would work.