The game back in the day didn’t have rare spawns that 500 other people want to kill too, that you need to do the content there. Rare spawns only dropped a small assortment of weak blue crap for the most part, and few people cared about them other than achievement hunters.
You had time to look up quest objectives and such and didn’t have to be too concerned with somebody else getting there before you, and if they did find that named quest enemy before you, it was a 5 minute wait for a respawn for you to get your turn.
EDIT: But hey if this is just for rep rewards… wait until next expansion. It’ll be a ghost town and you’ll have all the time in the world to solo all those rares.