As I see it, there are 2 big, substantive big problems with the redesign:

I.  The redesign HIDES replies by default, making it unlikely students will read them!  This is effectively a negative nudge as even if students understand that they COULD read replies, hiding them by default makes it unlikely they will select that option, leading to them missing opportunities to recover lost points by addressing instructor or student comments.

2.  The redesign lists posts "last to first" rather than "first to last" by default.  Not only does this make locating individual posts difficult, but it buries any "Sample Posts" the instructors make at the bottom of the page.

Unmotivated or struggling students will often use the first post they see as a template, which is why I like to post "Sample Posts" (AND "Sample Replies") for the first few weeks of class demonstrating what an "A" quality post (and reply) might look like.  Before I adopted this practice, it wasn't uncommon for the first student post to be F quality, and a fairly large number of students copy the F-quality template.

Together, these changes effectively hobble the Discussion forums as a learning tool.  In fact, they hobble them as even a DISCUSSION tool.

Student A Post:  X

Student B Reply: ~X (unread)

This is not a discussion!  A discussion involves two or more people exchanging ideas, but if Student A walks away after saying "X" and Student B walks away after saying "~X" then student B might as well just be talking to a wall.

Are there benefits to the redesign?  Frankly, I don't see any, but whatever the benefits, they don't excuse the drawbacks.  Discussion assignments used to be the backbone of my online Canvas courses.  Now?  They're a detriment; even if I drastically reduce the Discussion component of the course, I'm going to have a lot more students failing because Canvas actively makes it harder for them to complete the discussion assignment and easy for to mistake a halfassed mid-week post for a template.

Let's face facts; many students don't even bother to read the assignment instructions, but instead use other posts as templates.  Struggling or motivated students used to be able to use Sample Posts as good templates and regularly receive passing (C+) grades, but now?  Now I'll be handing out a bunch of Fs.  And it'll be the students' fault for not reading the instructions or reaching out for help.  But the discussion redesign enabled and encouraged this bad behavior.