What is your actual question?
"Is there a single change that could have made these hacks much harder?" seems like you are asking what could have been done to make it harder for the hacker to acquire the passwords (e.g: How do I properly secure my system?) but your example makes it look more like you want to know how you as a user can minimize the threat of stolen/leaked passwords.
In case you want to know how to make it harder on the hacker the answer is simple: No there is no magic trick that will make it harder for any hacker to compromise your system. It's an array of things you have to do.
What you as a user can do to minimize the threat of stolen passwords is also quite easy:
- Use 2FA wherever possible
- Use a password manager (KeepassX comes to mind)
If you do NOT want to use a password manager (for whatever reason) here are two things to consider when choosing a password:
Never use the same password twice!
You are probably not a person of special interest so the most probable way for you to get your password stolen is by these huge password leaks. By re-using your password across multiple platforms attackers can clearly map your username to your password and simply use that.
Increase the haystack
We have been told to create passwords which are hard for humans to remember but easy for machines to brute-force. Do not make your password a random string of letters, numbers and special characters, simply increase the size of the password, chose your favourite book quote or something similiar.
923_ixa13ff$/)" is an arguably worse password than "I like to take long hikes during spring, it's very relaxing"