There are, in total, more NCR quests than Legion's quests. However, many of the NCR quests present the player with an option that hurts the NCR.
Spoiler For example, you can get the group in Camp Golf addicted to Psycho or give fake intel back to the NCR about Cottonwood Cove. Not to mention that siding with the Powder Gangers is another way to kneecap the NCR. Or the hilarity of calling down the Helios laser on the NCR patrol.
So, there is a bias, but I don't think its too bad. My Legion character is having a blast sabotaging the efforts of the NCR right under their nose. And, as the game goes on, my character will outright start killing NCR on sight. From a gameplay perspective, I like that the Legion isn't that active in the game world. In too many games there is this perfect symmetry between factions. Personally, I think symmetry is boring. Its nice to be the bad guy, but also (kind of) the underdog.
And from a story standpoint, the NCR has a pretty bad rap.
Spoiler Everywhere you go, the NCR is in dire need of help. They can't control prisoners, they can't send more soldiers, they can't kill a handful of ants, they can't even protect their president from assassins. Playing for the NCR, you are basically singlehandedly preventing them from being defeated.
You really can't find a more corrupt and inefficient bunch of people around. They're really a nice foil for the brutal, yet disciplined and efficient, Legion.