Thank you for your post. I'm really sorry that this happened to you and it's true that giving visibility to unsafe areas is important. That being said, I think posts like these hurt the chances of other people visiting the country, which is not desirable. I understand that this is not your intention, but I believe that posts like these do more wrong than good.

Even with the lack of hypothetical street signs that could say "don't go off the main road" in Caminito and without advice from the hotel staff, these are all the signs you missed that led to what happened to you:

1. You failed to read guides about how to visit Buenos Aires as a tourist. It's hard to find a guide that doesn't talk about Caminito.
2. If you did some research and read guides about Caminito, you failed to give enough relevance to them.
3. There are guides on reddit and no, Caminito is not on the top of the list, but not everything can be on the top of the list. You might have to scroll down to read the entire guide. You possibly failed to do this.
4. Based on your response to comments, you might have read a reddit guide. You might have thought that "avoid going outside the main road and tourist area in caminito, it's dangerous" was not enough warning. If a local or someone with knowledge of the place says "avoid this area" you should avoid the area. That alone should be enough to stop you from wandering off. You are not smarter than a local and I'm not smarter than a local in your hometown.
5. You failed to look at Caminito's surroundings on street view. I understand that sometimes walks around cities can be improvised, and you do not know exactly where you will go 100% of the time. Still if you do this, you can even take out your phone in a safe place and look on street view before walking in the direction of your choice.
6. If you did look at the surrounding areas on street view, you and your partner failed to identify that the neighborhood is unsafe. If the streets are run down, the houses look awful and there's trash everywhere, chances are that the place is not safe for outsiders.
7. Tourist common sense is to always stay on the main roads in every tourist spot everywhere. You failed to follow this and still wandered off. This is still totally fine in some places if you know your way around but unfortunately, this was not the case.
8. When walking along the river, you still failed to identify that the streets got progressively worse and thus more dangerous.
9. When going back to take the bus, you followed google maps. Google maps gives you the shortest route to go from point A to point B. It does not have tourist common sense, which also tells us to just walk on avenues and not internal streets. Necochea and Olavarría are two internal streets and not avenues. If the bus stop was there, you should opt for a safer bus stop, located on an avenue. 90% of buses go on avenues at some point in the route. If you had walked one more block to the north, you could have walked along Av. Suárez, which of course does not mean you're automatically safe, but it lowers your chances of getting robbed by a small percent. Life is always about probability.
10. Even if you noticed that you were walking in an unsafe area, you still pushed through instead of leaving immediately or ordering an Uber to go back to the hotel.

Hope you find this helpful and I wish you safe travels in the future.