Rio and BsAs are completely different cities in every way. But no shadow of a doubt that rio is more violent.
If going to rio for holidays you most likely going to stay in Zona Sur or maybe around the Olegario Maciel and the beginning of Barra.
All definitely walkable but you d certainly need to be way more savvy than you would in Buenos Aires. Because foreigners are a more obvious target and because crime is more violent and commonplace. A switched on Carioca friend just told me yesterday that crime has gone up in the last few months.
I d say go for it walking around but only carry what you are ready to loose and try to blend in and be extra careful for thieves at the beach. Some beaches are safer like Leblon posto 12 (wealthy locals), vidigal beach (Sheraton) on weekdays (no stealing on ‘favela grounds’), joatinga (secluded difficult access), or praia Vermelha Urca (military base), Ipanema will depend on which posto. Won’t even go there with Copacabana apart from Leme which is slightly more local.
And also if you get in in rio after dark be careful with your phone and belongings in the Uber on the linha vermelha, the first few kms from Galeo airport to the zona sul.
The biggest risk I saw living in rio (apart from flooding) was being collateral damage in a shooting, wrong place wrong time. Not much you can do about that.
This said plenty of tourists go to rio all the time and love it, it’s just that you have to have your wits about you there
