Prior to 2012, that was probably true:
http://www.opensecrets.org/news/2010/09/opensecrets-battle-k...
But since then, the Koch brothers really ramped it up. The Koch brothers spent an estimated $412MM in the 2012 election alone, about an order of magnitude more than the amount Soros spent in the entire previous decade:
http://www.thenation.com/article/koch-brothers-spent-twice-m...
Combine the $412MM they spent in 2012 with the $900MM they want to spend in 2016, and that's ~$1.3 billion this decade, compared to Soros's ~$40 million in the last. That's not even close to the same level. And I haven't found any evidence that Soros is spending at the same level as the Koch brothers this decade.
He's also bought electronic voting corps and managed to get them into primaries like Utah. There were all kinds of shenanigans with them recently like denial of service to some voters.
I'm not sure not what you mean by the Koch's extensive network. They're either giving their money, or it is other people's money. They can't be held responsible for how other people donate their money. I don't hold Soros responsible for all the ACLU's actions, even if he is a major backer. When they ACLU stands up for something I believe in, I donate, but I'm certainly [not responsible] for all their actions, especially in years I don't donate.
http://www.discoverthenetworks.org/viewSubCategory.asp?id=12...