A constant balance of weapons is needed in Warzone so that players don't always use the same weapons. The typical day for Activision to perform this is Thursday, but it appears the company chose Wednesday. Since this event occurs in conjunction with a $300k tournament, this is problematic.
JGOD pointed out how easily it could upset players who are already used to the weapons as they are. Rather than at the beginning, it's right in the middle, so players have no time to adjust. Maybe there will be a new meta between rounds that pros will randomly figure out and keep to themselves.
Warzone weapon balance patch
It is easy to see why this is unfair to Warzone pros. After balancing, a meta is pretty much the best weapon, so no one knows what's changed or what's best whenever a new balance occurs. Players practice using the weapons as is, so a change in the middle of a high-stakes tournament is just odd.
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JGOD says it's $400k, but today's tournament is the $300K World Series of Warzone EU Duos event. You can watch it from this link. We believe that the tweet just contained a typo. That doesn't take away from how big of a deal it is.
Yes, some think a surprise update will make things fairer since now it's all about how good a player is. There is also an argument that the tool does not make the mechanic. This is all true but ignores the fact that weapons do make a difference.
Slightly better weapons can decide shootouts. While it is true that the tool does not make the mechanic, winning a match with a pistol is almost impossible no matter who you are. It will be interesting to see how things go, but pros will absolutely blame the update for many losses.