Even though Casteroids are better at collecting wood, mammoths can carry so much more, and have higher weight reduction. They also move faster and have a larger attack range. When gathering wood on a mammoth, I personally have found that it’s stomp, or left trigger (Xbox) attack gathers more than its main attack
Therisinosaurus collect wood very fast and very effective, but with it it becomes encumbered very fast too. Mammoth collect it not very fast, but it has big radius of attack and it can takes large amounts of wood with its high weight and weight reduction of wood in its inventory.