I think it's a stretch. "Mobility" doesn't mean you avoid getting hit. Lamar has as much mobility as any QB in the league, and he gets hit a ton. Both in and out of the pocket.
There's no ability to sell the idea that his wrist wouldn't have been hurt if he sat two months prior to that. That largely defies physics.
The argument for him sitting earlier in the season is that Browning, maybe, gave them a better chance to win, so they'd have a better record now than what they have. Maybe they don't get trounced by Tennessee if Browning is QB vs Burrow.
In reality though, its kind of a moot point. I like what Browning has done the last two weeks, but I think a month from now we'll have a different viewpoint. Josh Dobbs looks great in spurts too. So does Gardiner Minshew. There's regression coming, like every backup QB sees, and we'll see where the mean is at that point.