Sage Parāśara states this in the Daśādhyāya (Chapter 46), verse 157, here cited for you:

Following this, the Sage elaborates how to decide the stronger among them for the singular lordship of their signs.

Practically, in tradition, we do not treat the nodes as the lord of Lagna for examining the person’s body and physical health. We do employ them for examining mental health. Further, in reading the chart and the Ārūḍhas we first ascertain the stronger lord but do examine the placement and Ārūḍha of the weaker when its daśā arises. Viz. if Scorpio is the Lagna and Ketu is stronger than Mars, then the Ārūḍha formed by Ketu will be the most prominent. However, during the Mahadaśā or Antaradaśā of Mars, the placement of Mars and its Ārūḍha will temporarily manifest until the end of the daśā.