As you say, it is a job category that has existed for a long time. (In addition to examples already given, other specific titles off the top of my head spanning centuries: cigarette girls, playboy bunnies, bar girls, steak ladies, brand ambassadors, spokespersons, sign spinners, spokesmodels, …) As long as marketing has existed these jobs have also existed, they've just always before been typically given extremely specific names, often (especially in old fashioned ones) so specific even to specific genders.

I think it actually is useful to have a generic term for this as well across that multi-century spectrum of too specifically named and niched sub-jobs. It makes a useful lens to even better describe our own history. ("What's a cigarette girl? Well in the height of Big Tobacco the Tobacco companies would pay ladies, generally pretty ones, to be influencers selling cigarettes at other businesses such as a bars. Many of these influencers were not employees of the bars, they were more directly contractors for the Tobacco companies.")

I even think that the generic sense of revulsion many have to the specific word "influencer" is actually a useful part of that, too. These jobs were never pretty. Many were designed to be in the background marketing things to people like bad magic tricks designed to misdirect slight bits of money. Influencers are not necessarily a bad thing, and those are sometimes useful jobs in their own little ways, but having the generic term itself be a little revulsive is maybe a great reminder that they aren't always our (parasocial) friends, either, and are still trying to sell us stuff at the end of the day.

(A lot of people assumed cigarette girls worked for the bars or restaurants they found them in, when really that was a direct marketing arm of the cigarette companies. Alcohol companies to this day also hire a lot of "brand ambassadors" the now gender neutral, PC term that they prefer over "influencer", though "bar girls" was also a name for that not even that many decades back, and these influencers do the exact same thing: there are people in bars selling you alcohol, with the permission of the bar owners, of course, but employed by the marketing arms of the alcohol companies. Because they aren't bar employees they are legally "allowed" to often "get more personal" and sometimes don't even pretend to be "on the clock" working. Even more fun, some of these "brand ambassadors" for alchohol are only barely paid in like product because these "brand ambassadors" are doing it "on their own" "for fun" like a rewards program and multi-level marketing had a baby that decided selling alcohol to already drunk people was a perfect business model, which is also a fun way to skirt labor laws if you can get it and maybe not obvious with a title like "brand ambassador" but a bit easier to suspect if you call it "influencer".)