(Not a Teacher)
Q1 --- Yes, it's fine as written, as is the alternative sentence you've suggested. Personally, I would write it like this:
"As our capitalist economy grows, so does the gap between rich and poor." (You could simply use 'income gap' as well)
Q2 --- Here's how I would write it:
"Special care should be taken for the training of the middle-aged, who are the most underprivileged in the labor market."
Student or Learner