Someone else already replied, but about living within your means, lenders can look up other debts you have, and missed payments you have. And they all request access to your pay slips so they get a basic view of your income. In the end it's close to the credit score system, with the difference that someone who doesn't have any loans or credit cards willl also have a good score since they don't have any missing payments, and haven't gathered too much debt already, which makes sense.

Regarding your point of rent vs ownership. In the end you can still boil it down to needing a certain amount of money/month. Only part of it is your mortgage of course, you need to save up for bigger things, but it's not that different. And i don't even see this being relevant in this discussion, i don't see how the credit score system would predict you being up to being a house owner and setting money aside for bigger repairs.