Yeah, it's stupid how difficult it is to find people to level up to 70 with you. I always level up alone, because everyone else will already be at lvl. 70 grinding T1. Even at ten levels higher, the spike of mob damage and health will surely kill me.Since it's seemingly impossible to get a group of people on a regular basis to grind bounties/rifts I've just resorted to getting all classes to 70. The end game grind is a crazy by yourself.
Games shouldn't scale with the person with the highest level, but the one who created the game.
In that sense, D2 did it right.