I guess maybe I'm familiar enough with it to just slam it out. I don't recall any low droprate quests as bad as 5%. Although Blizzard has been screwing with stuff lately. Do you remember which quest it was? A lot of those can be skipped if they're too tedious. Like literally ALL the quests on that little island in the NE corner of the map with the ghost pirates underwater and the dragon whelps.
Again it breaks down to personal preference. I didn’t have an issue doing them at 120 on the toons I did them on. I felt like they took you out of the way when I just wanted to finish the zones. Too each his own. I liked it because I would finish the quest then be right there at the hubs for the quest on the new continent after I’ve finished all the quest on the first continent.
Congratulations on reaching Level 120! There are a myriad of new things to do. The first thing you should do is head to your faction hub ship where you have been doing your mission table quests and footholds to pick up and complete the quests necessary to unlock World Quests. World Quests will provide you an opportunity to grind reputation levels, acquire gear, and gather Azerite. There are tons of new things to do that we will cover in our Level 120 Battle Guide found here: Level 120 Battle Guide