It's not how many logons would eliminate the cron, but instead do you have traffic happening basically 24/7. For example, if you have no users from midnight to 5 am, none of the tasks that run in that time would run without cron or something else to execute those tasks. In addition, even if you were able to run it with traffic... if it's a 500 error, it would still fail to run. Again, you need to look at the server logs to figure out why the task triggers a 500 error. That will happen regardless if it's triggered via cron or running with traffic.
And v5 will be like v4 in terms running background activities. Cron is highly recommended as it's the most reliable method in case you don't have traffic during certain times.
If you don't know how to get or understand your server logs, you might want to use a third party resource to help. https://invisioncommunity.com/third-party/providers-directory/