Still smells like Favreau or someone else sat down to review what Season 3 *could* be, realized that the Darksaber story demanded a more culturally critical and characterization heavy story where Din would have to exit with a defined identity because of how Filoni had constructed the Darksaber story back in Rebels…
…and just deciding to ignore that story and argue some counterfactuals instead.
I mean, the first time we heard about the Darksaber being heavy was when Sabine trained with it and learned it would become lighter the more she mastered it. And there’s no way that they planned out Din getting it just to eventually pass it on to Bo Katan in a technicality, and there’s likely no way they had him struggle with its weight initially while planning that would mean he couldn’t keep it.
I still think that somewhere in Season 3’s development, someone had a negative reaction to the ideas of giving Din an epic story rather than an episodic one and to examining the Mandalorians in a less than flattering light, and the Season just sort of struggled once that avenue was cut off.