Mathematically 1 million atomic converters use 1 million times more energy than one of them, but also convert 1 million times as fast. So for example you're using 1 million times more energy to make a 2 second conversion into a 2 microsecond conversion, so you should avoid terraformed converters earlier in the game.
Later in the game, when you get lots of stone, you'll start to see it makes sense.