That's not the case at all. Assuming you have a decent level of skill in the games you can get 50-90 coins per game, so if you let your girls decay a little bit and spend their energy on games you can earn 200-360 coins per girl every 4 hours. That's plenty of time, and that's even assuming you have 0 coins to begin with and you don't roll on any gacha besides the basic one.