It all depends on the amounts being moved. Transfer pricing is complex because what is market rate in situation A is not market rate in situation B. $345 million could be a minor difference of a few percentage points on tens of billions in revenue.

Just like FDSGSG wrote above, I went through a sizeable tax dispute (for an individual, outside of the US) and won. I have a good understanding of tax law yet it was nothing more than a bullshit money grab. No merit, nothing. More along the line; that's a very nice outcome for you but we don't really like it -- so pay up regardless. Like trying to shake a tree.

In this case, I can imagine for Activision (as a publicly traded company) it is better to settle a case for an OK amount than take it to court and run through the process. You have to make a risk reward analysis of whether it's worth spending time and resources on.