Actually, they were not. The companion NPC in 1.0 was the Path Companion, who was a fellow member of Minfilia's Scion-predecessor organisation the Path of the Twelve, and thus they possesed the Echo like you and could thus speak with Primals like you could without danger of tempering (in fact, it was an ill-advised and unauthorised jaunt to Za'harak to meet Ifrit at your Path Companion's behest in 1.0 that Minfilia first discovered the Echo gave immunity to tempering in the first place).
They were story-wise of Ala Mhigan birth, and had a relative in the Ala Mhigan Resistance that you had to save during the story. Either way, they were last seen undergoing medical treatment at the ALC's Guild in Ul'dah after being shot by Gaius... and that was the last we saw or heard from them (it's assumed they perished in the Calamity).
Your retainer however is a completely different character, they're just a servant you hire to store your items for you and run sales on the Market Ward/Board on your behalf, which was the case even in 1.0. They're far from adventurer material though, which is why they're retainers in the first place, hardly the sharpest tools in the shed, but they're more than capable of mundane/boring tasks such as running bazaars and finding shinies. Retainer Ventures are pretty much just an extension of this. Hence why they wouldn't last ten seconds in say Sastasha or the Bowl of Embers. They'd suffer poor Avare's fate... only far faster.(Yes I know they can bring back gear and items from fairly high level trials and dungeons, even old raid items, but the development team has basically handwaved that and said "use your imagination" when asked about exactly how retainers can bring back stuff like White Raven Fragments from ventures).
And thus, this is also why Retainers specifically would most definetely not be a suitable candidate gameplay-wise to be able to be taken into dungeons and other instanced content. They'd be just too weak and would be too much trouble that it's worth in SE's eyes to have to code for (this is also why the Squadrons and Trusts have such limited use, Trusts the dungeons have to be specially coded for and Squadron AI has to be tailored for each dungeon it's allowed into).