“the boring work of backup”…
Backups may be boring, but they are essential and gives you a fallback position in case things go wrong. Without backups, you’re essentially playing Russian roulette with your site. It doesn’t even take very long, and reverting isn’t horrible or awful, it’s pretty easy.
WP veterans take backups, test upgrades on non-production servers, and when they’re happy do the upgrade. Most ‘ordinary’ people don’t have access to multiple servers or even local development environments, in which case the best way to mitigate your risk is to have a backup
If you have access to the command line, then doing a complete backup is as easy as:
tar czvf yoursite_backup.tar.gz /path/to/your/wordpressmysqldump -u <username> -p <database name> > mysqlbackup.sql
Reverting is as easy as unarchiving your WP backup to your WP directory and importing the MySQL dump into your database.