> Most people who answer telephones for a living are not paid to answer telephones. They're paid to answer customers.
If I'm speaking to someone who's worked too much for their capacity (whatever that is) and I get a curt, wrong, or bad-mannered answer I'm very likely to take my business elsewhere
(Warning: anecdote) I've just phoned my son's school to tell them he's poorly and won't be there today. The receptionist who answered the phone is "the grumpy one" (there are two at this school, the other one is lovely).
Of course it's possible that the grumpy one could well morph into being lovely if only they were given more time off, but I doubt it. I've spoken with both of them dozens of times, and it's utterly predictable, one is always lovely, one always isn't. Some people are great with customers, others just aren't.
> some positions do need to fill shifts and it is what it is, but you can always split them between more people
There are small businesses where teams are, unsurprisingly, small. Having worked both with and in such places, I'm not sure how feasible the "split between more people" actually is.