You're talking about the solo duty against the Warriors of Darkness where Alisaie creates a blade of light, right? If so there was absolutely no mention of Red Mage, and it looked completely different, both in terms of VFX, animation, and aesthetic. Even the auto-attack animations are just the PLD ones. Obviously it's understandable how people immediately assumed sword + magic = Red Mage confirmed, but since your argument is about production itself, Red Mage as we know it was only properly debuted on Stormblood's release, when you get access to the job and Alisaie gets an actual Red Mage weapon in MSQ, if my memory serves right.
So that was... 6 months after it was officially announced? Plenty of time to gather feedback if it needed it. But Red Mage was a lot less ambitious and daring with its visuals than Pictomancer, which is doing something completely new visually, so I doubt the players' reaction was as divisive at the time.
I'm honestly still scratching my head over this. Obviously, the department who worked on the CGI trailer are not the same people who worked on the VFX themselves. Obviously, the CGI trailers are never accurately depicting jobs (or characters, or even when the lines in the trailer are said in MSQ... unless Emet-Selch is secretly a Gremlin).
But surely, surely someone in production must have looked at both and thought "These do not look the same at all. Players will have things to say about this." (especially when it takes so much screen time in the full trailer). That's why I'm a bit startled that they're rushing the Pictomancer debut, when I don't think it would have been an issue to wait until 7.0 for Krile to get her paintbrush.
Then again, we don't know what the schedules of each department look like, so it could very well be that it was simply just not possible to delay the debut, either because 6.55 MSQ was already set in stone, or because the full trailer was only shown to the production team very, very late.