Good posture is always important, but (a big one) you do not want to be posing either.
Good stance/posture is not the most important thing! It has to be integrated with head movement, upper torso movement, side to side movement, in and out movement, angles, speed, and years of experience.
Some of you sound like you are saying, "Mr Newbie is fast and has great posture, he'll be ready for Floyd in a couple of years."
How do you explain the success Martinez or Emanuel Augustus had?