Talk:D.R.A.G.M.A./@comment-1418880-20150204072400/@comment-1763304-20150625134217

"They also had nearly impenetrable skin; even Zilla jr. could do little more than stall their assault. They also had the ability to rapidly reproduce. In an alternate timeline, into which HEAT was drawn, the D.R.A.G.M.A.'s had taken over the planet, decimating humanity and wiping out Earth's mutations, including Zilla Jr."

And furthermore, this even mentions that their hide is "nearly impenetrable," so I doubt any form of Godzilla could break through it. And these things killed off every mutation in the future, not just Zilla Junior. So that implies even the Japanese Godzilla and Toho kaiju were killed off when you think about it. (That would be an interesting theory to explore further in fanfiction.)