Currently, the three playing on the right are David Savard, Johnathan Kovacevic, and Kaiden Guhle. And number 21, although left-handed, is doing an excellent job.
This is the main reason why the two journalists believe that Barron could be sacrificed. According to them, he has more value now than he will in a few years, and other defensemen do a better job than him.
We know that Barron has high offensive potential, but it's tough in his own zone. When he starts getting hit, he loses confidence, and it becomes laborious. He is still young, but he doesn't have the same utility as Guhle, Xhekaj, Harris, and others.
Furthermore, Guhle's performance on the right would greatly help the Canadiens take more time to properly develop the two future pillars on the right, namely David Reinbacher and Logan Mailloux.