Some instances allow to sort by contraversy.

We're ultimately talking about which order comments should appear on a post. I don't think controversial sort should be default, and I don't want to read the most controversial comments all the time. I think the comments that generate the best discussion and/or are the most valuable should float to the top naturally. Ignoring down votes does this, with the added benefits of removing the possible toxic effects of down votes.

Isn’t showing only upvotes is default in Jerboa?

Dunno, I don't use it. Don't need to, my instance doesn't allow downvotes. If I needed to move from Blahaj for some reason, I might look into it, might not.