Exactly. Its no big issue but its a bit annoying. Especially since Ridley seems to be taking inspiration from what JC brought to the table with ALIENS.
Now obviously in the shot with Katherine, we can't see the entire gun so they might have modified the F90 further than what we can see.
And the shot with what appears to be blatant AR15 variants of some sort is a bit more annoying because the AR15 is even more so recognizable than the F90/AUG.
Its possible the shot with the AR15s is a flashback of some sort. Guy Pearce did say he was going to reprise his role as Peter Weyland. And if its a flashback with young Peter Weyland, that shot may take place in 2020 or some nearby year where we'll still be using AR15s.
For reference Peter Weyland's Ted Talk takes place in 2023.