They were not complaining last tier when the deciding factor was who gets to do split runs first. Not to say that the other dude doesn't have a point, but the impact of the headstart and who benefits from it heavily changes based on the last boss tuning and the time when that boss gets killed.
If the last boss can get killed before the first reset, then yes, being able to watch strats and being able in some cases to get to a boss that has been hotfixed can definitely be an important advantage for EU that is then able to get to the last boss quicker and spend more time on in before the reset. If the boss can be killed without an higher ilvl, then the ball is clearly on EU's side at that time. Jaina was the perfect example of that.
On the other end, when a last boss with very poor tuning cannot be killed before the reset but only requires split runs to kill after the reset, then the (second) headstart is an insane advantage that almost simply gives the victory to the side who resets first, US in that case. Denathrius was the perfect example of this. G'huun would have very likely been the same without Limit's mistake.
What I hope for this tier is that Blizzard will have tuned Silvanas better than Denathrius or other previous poorly tuned bosses so that she doesn't go down right before or after the reset, and we don't see another tier where the headstart ends up being the decisive factor.