It is not about swords or staffs. The probability of items dropping is the same as how items in heroic bosses drop.
Baron Fuego will probably not drop a Guardian Relic the first time you beat him. It would need several kills before he drops one.
A single heroic boss does not drop only the same item over and over. They drop a RANGE of items starting from sword and staffs until the most advanced for them.
This is the same way the new world boss drop of plans works.



