请教一个英语句子结构问题

整体分析：

状语和主谓宾部分非常明显，下面对定语从句进行分析。
关系词where，剩下的部分分成下面几个语意结构：
our welfare system has evolved
from being based on the principle of unemployment insurance
to providing a permanent top-up to wages set so low they provide insufficient means by which to support a family
前两个结构也比较显而易见，下面分析第三个：
providing a permanent top-up to wages (set so low they provide insufficient means by which to support a family)
括号内是wages的后置定语，是一个结果状语“so...that...”结构，省略了that。对语句进行还原应该是：the wages are set so low that they provide insufficient means by which to support a family，这样就很容易看出they其实就是wages。
下面对they provide insufficient means by which to support a family进行分析：
by which to support a family是means的后置定语，which指的就是means，字面意思是“设置得很低的薪水提供了不足够的方式，通过这种不足够的方式来养家”，其实就是说薪水不足以养家。