The Titans were lessened by their participation in the Cosmos project. They were forced to embody and support fixed aspects of the architecture of Kronos's world: They entered as creators but became as much prisoners as those that came after them.
In the end, the dimunition and split attention forced upon them in the Cosmos led to their undoing. The much weaker Olympians and their allies were able to exploit flaws and weaknesses in the universe that the titans had been blinded to by their perspective. Those that opposed the Olympians' coup were imprisoned in the extradimensional realm within Tartarus.
The titans avatars (only a part of their vastness can be seen, even in their diminished state within the Cosmos) appear as humanoid giants. Their primary self-nodes often reside at other places in the universe: for instance, Hyperion's intellect resides in a quantum collective constructed in the event horizon of the supermassive black hole at the center of the Milky Way galaxy, while Theia's is distributed in the stellar nursery of the Orion Nebula.