Not all plain steel strings are the same. Some feel stiffer and are less pleasant to bend, and some snap more easily. Elixir is the golden standard.
Buying a bunch of 012's is a great idea for anyone who plays 009 sets on their electric, since 009 sets usually come with a 011 for B, which is just plain wrong. A 012 B string has the same tension as a 009 E string, so it is objectively the right choice. I have no idea what string manufacturers are smoking.