He used clones because body hopping and altering them takes up energy. Emet doesn't enjoy using any of his aether/power if he doesn't need to. It's why he chose to live as the person he originally possssed until that body dies. Unlike Lahabreha and Elidibus who frequently body hop. To the point Lahabreha did it so much that he basically was burning the candle at both ends. They're only immortal due to the fact you can't easily kill such an aetherical dense person as an Ascian. Along with anyone who has the echo. Or at least that's what they hint at with Zenos since he didn't die and has a fake one. Though it could also be due to the fact Emet is his biological great grandfather.
As Pawpaw stated the Crystal Tower raids was optional and now is a road block soon after completing 2.0. When they made it mandatory due to how the MSQ unfolds if you hadn't done it by the start of 5.3 and you were at that point in the MSQ you'd have to go and unlock it.