剛去查出來了，你說得對， 他的觀察不適用於大樹。

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3979699/

both biomechanical models agreed with da Vinci's rule when the branching angles of daughter branches and the weights of lateral daughter branches were small; however, the models deviated from da Vinci's rule as the weights and/or the branching angles of lateral daughter branches increased. 

我最近連讀2本達芬奇的書，作者們偏向性都太強了--隻給出Leonardo da Vinci's Rule，再誇他是天才， 而不說具體這個Rule的適用範圍很小。