I like this advice and the reasoning you've given but I beg to disagree. In my personal experience, the act of trying to get into the big pubs itself improved my writing by leaps and bounds.

It took me 7 tries to get into Ascent and if I hadn't kept trying for it, my writing wouldn't have improved as much as it has.

It's the same with Better Humans and Mind Cafe. I'd say - try for the biggest pubs but don't let rejection faze you.