I don't know... take Morphy. No books, no regular competition, and he was at least master strength (some say 2500 even).
For others... 1200? Maybe less?
The part that stood out to me about Petrosianic's advice was access to strong players and study being fun. These are the things that will really help you. I guess it depends what you consider work and what's fun. You said you dig around on the forum for tips sometimes, that's a start.
Yeah, it does depend on how you define "study" -- and of course, if you are a chess genius or not.
Also this may sound dumb, but I think that in some sense the "purest" way to play chess is between two people who haven't studied the ideas of others to improve at chess. I like the idea of figuring it out on my own.
I used to think like that in my 20's. But I liked to win. I won my share of games against other dabblers, but felt embarrassed when losing. I finally looked at a book which was aimed at people my level. It suggested one opening as white, and two defenses as black. With minimal effort, my game improved.
While I didn't stick with these openings (tough to do against significantly better players), they taught me a lot about strategy and planning, development and piece coordination. It opened up a whole new world of appreciation for the game.
While "figuring it out on (one's) own" has some appeal, when trying to re-invent the wagon, it's helpful if someone takes you aside and says, "Pssst ... buddy .... Make the wheels round, put 'em on the bottom, and, oh, yeah ... the horses go in the front.