Re: devops199 said they were a newbie
"the target of criticism since the late 19th century"
That's the consequence of grammarians trying to force-fit the grammar of another language, Latin, onto English.
I suspect that underlying all these issues is a sense not of number but of the personal vs the impersonal. The "singular" is more personal than the "plural". Where a less personal form is needed we instinctively use the "plural", hence not only the singular they but also the royal we.
I wonder what the use of the impersonal "you" ways about us. Have we simply become too impersonal in our dealings with others or is the etiquette too complicated: I can thou thee but don't thee thou me was how to express it to a junior.