That statement really surprises me. Especially since, about a year and a half before you removed it, one of the product managers had noted that more documentation was needed.
That wouldn’t have made much sense if it had already been disabled back then.
I think the setting was default: false even when it was added 10 years ago:
Could it be that there was a job that enabled bootstrap mode instead?
So had bootstrap mode been disabled before it was removed?