Isn't the power consumption needed to create pure/no-blemish lab diamonds so great, that this wouldn't be feasible to scale.

Lab diamonds are used in huge quantities (ie. By the bucketful ) for making cutting tools like saws and drill bits.

I believe the main difficulty is making large and pure diamonds. Making small low purity diamonds is cheap and easy to scale.

massive crushing pressure is not the only way to create diamond particles.