"To get by" means to earn enough money to meet current expenses and implies a struggle. "To get ahead" means to earn enough money to meet expenses and to be able to save some for the future.

太多美国人比之前更需要努力工作勉强过活，更不用说是要富余了。

Just to get by means they are struggling to keep their life in order. Bills to be paid and I'm sure that quite refers to their famiky. Making sure they have enough money to support their family to feed, clothe, and educate them. Let alone get ahead means they aren't even worried about having a lot of money because they are focused on just having enough money for their family. Getting ahead in that quote would refer to having more money to take care of their family finances and extra money for shopping, travel, savings, and the like.