I disagree, you simply cannot push t3 armies against a billy and TMD doesn't counter this as every inch of ground you take you have to spam up 4 more TMD (because if the Billy is fired infront of the TMD, it will detonate before the TMD can reload). If you are pushing with EXPs and don't have air, all your mobile AA will get wiped away from the Billy.
The energy cost of the Billy is 4 t3 pgens (13k mass) factor in the Billy upgrade cost as well as its missile it rounds out to 20k mass, the first billy is almost always a surprise thus with a couple of Janus you can wipe away the TMD in the way, and destroy a whole core base, after that it simply costs 3k mass per billy, thats 3k mass to wipe every subsequent t3 army on the field, 3k mass to Billy another core base when the fatboy / sat clears the TMD. Even if your only able to use 3 billies effectively, you simply have to destroy 9k mass on average with the billy to break even. (8 percies worth of mass).
I think this game is a perfect example of the Billies power, Snoogs mass spent to mass killed ratio with his com is something like 1:3, and if we factor in that he was air and had spare t3 pgens his ratio would be more like 1:6.