I'm playing around with Gaea at the moment, and I have to say, that I'm really impressed. Daniil's plugin is absolutely fantastic, no doubt, but I'd say, that the possibilities in Gaea are way more than just erosion.
There are so many other terrain structures, you can create quite easily, that would be quite hard to reproduce in TG alone.
Digitalguru explained a working method for exporting Gaea terrains into TG here:
https://planetside.co.uk/forums/index.php/topic,27731.msg275659.html#msg275659I tried it, and it works like a charm. All the details are there, if you choose a high resolution. I exported 8k maps, and it looks beautiful. And it's easy to choose all the maps you want, and export everything at once.
Nevertheless it would be cool, if there would be some sort of a bridge to connect between Gaea (or other apps) and TG.