Scheduled Tasks don't run on schedule

None of our scheduled tasks run on time. Not a single task. Should we switch to cron 100%? or perhaps switch to triggered tasks and an external scheduler?

Has anyone else experienced this?

How far off are you seeing?

In the documentation Scheduling a Task, it states:

A scheduled task can take up to 10 minutes past the scheduled time to execute.

If you need precise execution times, then yes, you should switch to triggered tasks with an external scheduler.