Exactly. People can brag about the difference of the quality of the squads or how more expensive the City one is as much as they want but the reality is the Brazilian team lost the game already with the way they wanted to play..very brave but very naive and not up to the reality of the real football standards of today..
You can't put forward "reality" and end your post with a blanket statement like " "not up to the reality of the real football standards".
It's one game, against literally the best team in the world. It's not enough to completely bury this idea forever. If anything, the fact they were in this position to play against the best team of the world, should be enough to inspire other coach to experiment with this idea and see what they can do with it.
I personally don't think it's going to be effective in modern football and I actually agree with you but Fluminense results are intriguing enough to make coach around the world at least consider this a viable path to experiment with.
Let's say you are completely dominated, you have 30 minutes to completely change a game, I'd like to see teams try something else than "let's play with 5 forwards and hoof the ball in the box"