1. This change is much smaller and less destructive than digg's big change (although the long term effects can be just as destructive).
2. When Digg's redesign caused an exodus, Reddit was extremely well known as "that ugly digg clone" and "this digg link was on Reddit yesterday". Reddit doesn't have a well known established "number two" the way digg did. Raddleme is a leftist fringe site, voat is a racist fringe site, HN is a technology fringe site. Discord servers rely on Reddit for discoverability and member vetting. When this has been discussed before, I've never seen a viable candidate mentioned. Since the only people who can leave are people who only use fringe topics, Reddit won't be able to loose critical mass and then the fringers will have to come back.
On the other hand, these changes appear to be a step into the Twitter/Instagram/facebook market. I'm curious if Reddit will be ready in time to take advantage of this upcoming Facebook exodus, also if there will even be an exodus.