…which will make it shine in air tests. Now imagine shining a flashlight into dense fog. You can barely see, so you crank up the brightness tenfold. Congrats, now you're totally blinded by glowing fog!…
Is it possible that the FCC relaxed some regulations for VLF transmitters, especially their power? Sure. Will increased power be beneficial in real world metal detecting scenarios? Only in some soils, and far away from the structures. Oh, and just like in my flashlight example, extra power works better if you offset transmitter and receiver, in this case – in 2-box machines. That's pretty much impossible with DD coils.