DY: Going back to that Rashbam, it is exactly his point there that make “Yashar V’Tov” and morality subjective. By the rules in place, Runia has no right to the land. Subjectively based on Runia’s wealth (or lack thereof) it was decided that it would be more “Yashar” to waive Bar Metzra.
The same would be true in the other example that you mentioned. Another example is Tosfos by Issur Giurah, where the needs of Rava’s Yeshiva overrode the Mitzva L’Kayem Diveri HaMes (brought in many places, including BB 149a IIRC). That is a subjective application of morality.