i have the opposite opinion of Jackson. i very rarely hear English, and Argentines actually get frustrated 90% of the time if they find out you aren't a native speaker. like, they just give up. i was at a brewery last night and a 10-year-old kid rolled his bike in and said something to me, but there was a music speaker nearby, so i said "otra vez?" and he looked at me, and said, esta bien (nevermind)! this is almost always the case with Argentine people in BsAs who have zero English, can't manage to speak International Spanish to tourists at their business, and i suspect they have never traveled very far.
i would highly recommend if you're putting so many hours into learning the dog poop scene, that you get on DuoLingo and do 30 mins a day, and learn basics. every city i go to i try to learn the basics of bathroom, sorry, please, thank you, beer, food, help, etc.
you're in for a rough time if you think BsAs folks speak English, the older people do, but anyone under 40 i haven't seen it at all. like 95% Spanish-only. of course if you go to the Hilton and sit in their lobby and go to the nearest restaurant, you'll have educated folks in the tourism industry. but i don't travel that way, and find it a very sanitized, Instagram way of "traveling" that is vapid and unfulfilling.