Cron has given me a ton of headaches. Between skipped jobs on reboots and DST, inability to properly express some dates ("First Sunday of the Month" is a common one), and worst of all, complete inability to prevent the same job from running multiple times at once, it's been regular headaches for a shop who has leaned very heavily on it. Some cron daemons handle some of these things, but they're not standard, and AIX's cron daemon definitely doesn't have these features. Every job has to be wrapped in a bespoke script to manage things that systemd already does, but much worse.

systemd has given me many headaches, but as a whole, it has saved me far fewer headaches than it has given me.