The US is definitely one of the most diverse large countries. India is probably more diverse along language lines. China is definitely not along any dimension. Even the EU states (that depend on US for defense and use oil to power their economies) are less diverse.
The US is a far more free country now than it was 100 years ago or at any point since the introduction of agriculture.
Compared to one hundred years ago, there's political changes:
- Minorities and women can vote
- Labor rights
- Consumer protections (No more debtor prisons, etc.)
And tech changes:
- People aren't stuck on their farms all day
- Families aren't stuck doing chores all day
- Birth control has allowed sexual freedom
- The trains, planes, cars and the internet has allowed freedom of location
Etc.
For example does enabling a person's ability to vote actually increase one's liberty in a corrupt/narrow system.