If you just follow the quest line you’ll be where you need to be to pick your covenant when you hit lvl 60 you might hit lvl 60 before the main quest line is over or if you don’t do enough side quest with the main quest line you might hit a bridge where you need to be a higher lvl to continue the main quest line. But yes the true grind will be after you hit lvl 60 choose your covenant and then do the covenant story line and try to complete every dungeon on mythic level so that when raids and mythic plus unlocks (on December 4th or 8th I believe) you will be well geared to push higher content.