Years back when I started seriously trying to get a book deal I made the mistake of reading a newspaper. It listed the bestsellers and my gaze lighted upon two of the worthies carrying the torch of American culture by virtue of being bestselling authors: One was a professional wrestler. The other was a pornographic movie actress.
Let that sink in for a bit.
Doubtless these worthies had more going for them than copious amounts of exposed flesh. I'll let others wring their hands about the corrosive effect of such upon the nation's morality.
The point I'm making today is that when these folks sat down to write, the writers mantras I've inflicted upon you were not considered. As you learn to write and try to write better, you'll see where others have flouted what constitutes good writing and have still acquired a book deal.
The lesson to learn from this is not to toss away learning to write and write well, but to keep in mind that publishing is a multidimensional enterprise. What works for one person won't for another. Unless you intend to start taking off your clothes... and getting into the wrestling ring (what? You were thinking something else?) you should put some thought into how you are writing and how to write well.
Despite a certain archness of tone, I'm not really begrudging the successful author who ignores the writers mantras. There's many roads to success and some leverage writing mantras and others do not. You have to decide for yourself how you'll proceed.
The main thing is not to get discouraged when you learn someone else succeeds by taking their clothes off.