The Tosefta was obviously listing certain דרכי אמורי that we shouldn't follow, not the other way around, looking for Jewish customs if there are similar practices anywhere in the world throughout history and by default assuming it to be the root for our traditions, like we so often see by ones who are majorly influenced by goyish culture today and are quick to assume the same about our forefathers too.
There is a different school of thought which you aren’t accounting for. While assuming that the dancing around the fire didn’t
originate in the fashion of the various עע״ז, nonetheless it’s too similar to it condone as something worthwhile. Better to stay away.
Many Gedolim railed against the various “minhagim” associated with lag, as you are well aware.