I've done onprem highly available MySQL for years, and getting the whole master/slave thing go just right during server upgrades was really challenging. On AWS upgrading MySQL server ("Aurora") is really just a few clicks. It can even do blue/green deployment for you, where you temporarily get the whole setup replicated and in sync so you can verify that everything went OK before switching over. Disaster recovery (regular backups to off site & ability to restore quickly) is also hard to get right if you have to do it yourself.