I guess few people would notice this difference, but I think it's better to avoid changing it unless there's a good reason to do so. Personally, I also feel the original formatting better -- especially because the "xx more child contexts..." line is aligned with the other child contexts at the same level.
Attached a v2 patch to restore the original indentation. What do you think?
Thanks for noticing the issue. I also agree with you all about using 1-based levels consistently in memory context outputs including pg_log_backend_memory_contexts.