If techs take too long to discover, you might end up with a conquest victory with swordsmen
To reasonably slow down the pace of research, I modded my game like so :
Writing doesn't allow to to trade communications ; radio does. Great to avoid everyone to know all the others by 1000 BC. Technology spread will slow down big time, except if you're on a Pangaea.
Mapmaking doesn't allow to trade maps. Navigation does. Great to avoid Civs to mave their unts in the direction of a Civ they know of, without having contacted them.