Crontab could be confusing at first glance but 100 lines (literally) of man page have everything including examples. In my exerience they covers 99% of use cases unless you need something REALLY fancy.

And you have cron on every system including BSD and not sure but probably also AIX/Sun/etc. It is universal and everyone knows about it. If your server doing something weird your probably will check crontab, not some obscure systemd subsystem almost no one knows about.

Instead using standart solutions (POSIX by the way) systemd again found NIH problem with cron and added one more tool in init combain.