Based on last two sentence it's not worth responding but i still will.What percentage of the car development budget was their over spend? That would be a more relevant metric.
How many other teams made this "mistake"?
Dodgiest team on the grid.
The loudest rumor is that they didn't included Newey's salary since he is in top 3 earners but the contract they have with Newey makes him outsourced partner and couldn't be excluded. They had this type of contract with him for years and if that is right they will surely change it this season. So the additional cost that pushed them from way below cost cap to over it didn't come out of development budget since it was accounting error and not overspend.
People fail to understand that a lot of things are excluded from the budget and team like Mercedes with all the additional costs for drivers salary, top 3 earners, marketing budget and others things that are excluded still spend a lot more than a team like Haas.
So narative that Red Bull gained some sort of big advantage by going 400k pounds over all other teams which spend the same is very naive since it's not the case.
Their first submission as I said was 5 mil below, many teams probably left themselves even more leeway and some others probably went much more to the limit and the money spend which is included in the cost cap from team to team varied in the millions. Not even mentioning costs that are excluded.
And you say that 400k significantly impacted results in those circumstances...
Yes in the end they were over and have to pay big fine and are heavily impacted from reduction of wind tunnel testing but those punishment have much bigger negative impact that the money overspend could have positive impact. To be fair like all punishments should have.