Have you read the article? The fourth paragraph lists improvements systemd timers bring over cron:

Cron is easy, very simple and robust mechanism to execute periodic tasks on a *nix server, and is available by default on all popular Linux distributions. However, cron suffers from some issues:

• If the system is down when the cron needs to run, the cron will be missed

• There is no built-in status monitoring

• There are no built-in logs

• If you want to execute pre/post commands (for example by pinging an external service for success/failure) you have to do it inside the script itself

All of these issues are addressed with systemd services and timers, as the authors explains in details.