At the risk of being the mosquito at the picnic, these overarching numbers have little relevance to the Dems' goal of taking back the House, the Senate or both.
Only a relatively small handful of House and Senate seats will truly be in play. The reason for this is the post-2000 census redistricting by state legislatures, which generally opted to create "safe" House seats in their states. Even in the case of the Senate, overarching numbers can paint a misleading picture. Consider these tidbits from February's Harper's Index:
Margin by which total votes for Democrats in the last three Senate elections exceeded those for Republicans ...... 2,900,000
Number of seats won by Democrats and Republicans, respectively ....... 46, 56