macOS, Can't disable default calendar alerts
UPDATE:  Cancel all of this.  I just realized today that all my default 1-hour alerts are again back on my desktop device calendars.  However they are NOT back on my iPhone.  iOS shows no default 1-hour alert, but macOS does on both laptop and desktop (High Sierra and Sierra, respectively).
So I don't know if this is a bug in macOS Calendar or iCloud or what, but it's still driving me nuts.  Original "answer" follows.

At the moment it appears I have finally solved this.  Apparently I must not have tried changing all the alerts from my phone after all though I thought I had.  Changing them from macOS simply did not work, but changing them all one by one from the phone, seems to have done the trick.  This morning my usual alert at 9am that always would go off at 8am, did not.  It went off at 9am as desired.  So unless I find things revert back again... I'm going to call this the solution.

Change the alerts from an iOS device, not macOS.