So what exactly are Conquistador good at?

They have low HP and get countered into oblivion by every single trash unit. Very expensive too and low accuracy

Their range is bad so they can even get beat out by archers in some civs.

I find the hand cannoneer and the Janissary much better units because they dont get pwn by pikes and skirms as much and seem somehow more accurate

Any tips for using them?

I love using the Spanish their tech tree and civ bonus are amazing.

I know they have good dmg against infantry but it seems that no one uses the militia line after castle age(besides some infantry civs)