Node yields assume the base harvest HP from game data (e.g. 1000 for Redwood trees, 620 for Metal nodes). In-game, trees and rocks with bAllowHarvestHealthScaling have per-instance HP that varies with the node's size, so actual yields per node will vary. The values shown represent the average.
The Giganotosaurus is an effective Umbra Scale harvester. The Mek is another good option. Rankings are based on actual game file data.