You get it.
In America we can use first names with total strangers, so whether it's Frances or Francis it sounds the same and gender, etc., etc. is irrelevant when addressing them.
But if you come from a culture where using first names is not always welcome in all circumstances, especially from older people or traditionalists, titles matter. When I worked in Duesseldorf, I would never in a million years have called my colleague and the eminence grise of the company "Ludwig". He was "Herr Busch," and he always will be.
I don't bother with last names in my conversations with Upwork clients. No one has ever, as far as I can tell, been offended, no matter what country they hail from.