There's a difference between GregTech making other mods more difficult to use, and Terrafirmacraft making other mods more difficult to use.
Industrialcraft is made more "difficult" by GregTech because it makes the macerator more expensive.
Industrialcraft is made more difficult by TFC because TFC removes the vanilla terrain generator completely and replaces it with its own. And that custom terrain generator does not spawn vanilla stone. Not a single block, not anywhere. It doesn't exist. And as such, Industrialcraft cannot generate its ores anywhere, meaning it is completely unusable. UNLESS someone makes a port of IC2 that uses TFC's copper, tin, and pitchblende (uranium) ores. And then you still don't have any rubber trees, which would have to be added as well, since the way trees are handled is completely different in TFC too.
TFC is not a content mod, it's a total conversion. Mods made for vanilla Minecraft are not compatible unless coverted. Period.