I have also played as Eriador (one month ago). Yes, it is easy. No, their settlements are not growing fast. I have won the game with only low tier units (militia archers+spearmen, woodsmen, general's cavalry, merchant cavalry). I was really eager to get my hands on greenway footmen and cavalry, but I only manage to build one unit in the whole game before I was victorious (turn 112)...I have had a good general in Bree (7+ respect) and low taxes for the whole game (except when some building was finished). I played short campaign.
If I have played the long one, there would be another problem with Greenway units. I would start building them around turn 100 or so, but how would I use them? They are regional units, so I can not retrain them where I need them, where the war rages. Since I need so many captured settlements to win the long campaign it is only logical I would be a loooooong way from Bree. Those Greenways would not be really usable in fights because of no possible retraining.
How to solve this problem? Grow faster! Fast enough to be able to use Greenways against Gundabad, Misty Mountains and Isengard.
btw. Same problem with Dale regional units. Athala Rangers or Horseguards will never see the battle

. In the time I can recruit them, I am already fighting long way from their regions...