You say that you think the parse is accurate because the dreadnaught is dying in the same amount of time..

Well, after doing this fight enough, everyone really just starts to memorize how long you have in the dreaded phase 3 dps race before phase 4 starts. If I am doing a run with lesser-geared people, I will push out more dps (pop more cooldowns) on phase 3 than I normally would because I know I need to make up for someone who is not as geared as me. That means popping my beloved Enkindle (SMN 5 min cooldown) when I might have saved it for a later time. I'll also probably pop Contagion instead of saving it for phase 4. Other people in your group probably alter their cooldowns (may or may not use raging strikes, for example) depending on how they perceive the length of phase 3 going. It's game over if you don't kill the dreadnaught before phase 4, so of course you're always going to kill it at the same time if your group wants to push on. I would not trust parsers specifically because "well, it's dying at the same time."