Apex quest line isn't here to make you earn XP, it is here to get you gear (exodor scout one) and new skills.
It is strongly advised to do it once you reach lvl 65 because it will make your character way stronger until you reach higher lvl and get new gear.
If you die a lot as you say, maybe you should check your dodge skills, and depending on your classes, you even may have some skills that replenish some of your hp.
After you complete this quest line, you'll get the one that really gives XP (untill lvl ~68) but you can do Macellarius Catacombs in parallel to grind more XP.
May I ask you what are your classes?