I was targetted after Consentus' database breach around 2011 (they got access because one of the Consentus admins used the same password on some other RS fansite that got compromised). I know they targetted me because someone uploaded the chat logs to pastebin where the hacker, who was trying to sell the information, named me as a wealthy player in his selling argument. They never did manage to get into my account, though.
Never use the same password twice on anything that matters to you and you will probably be fine. 2FA on your email accounts. But how do you memorize all your usernames and passwords? Use a password manager! Stronger passwords help in case the database gets breached. If you have a strong password, chances are it will take too long to find its match (if the hashing algorithm is even remotely modern, it's all done through brute force, i.e. trying millions of passwords every second until it's found; often dictionary list based).
Jagex's account recovery system is the most concerning part in all of this, especially if they rely on such basic information such as IP and ISP (they are by no means secret on the internet and you cannot hide it unless you're using a VPN or proxy, which is a security problem of itself), name and country.