Republican-leaning groups merely made Republican challengers competitive

Even the NY Times citing the Kantar Media group concedes this:

The most recent numbers available, through Friday, showed that Democratic candidates and their allies spent $142 million on television advertising across all House races in the general election, compared with $119 million by Republican candidates and their backers. In the Senate, Republican candidates and their allies outspent Democrats, $159 million to $120 million.

The Democratic advantage on television spending in House races was something of a revelation, given all the attention that has been garnered this year by the staggering expenditures by Republican-oriented independent groups after a Supreme Court ruling in January that lifted restrictions on corporate political spending.

But it appears that the Republican-leaning groups were able to make a significant impact in many House races by leveling the playing field for underfinanced Republican challengers, who in previous elections might have had little chance against Democratic incumbents. . . .

Total according to the NY Times is $262 million for Democrats versus $278 million for Republicans. Republicans thus had 6 percent more to spend.