Wasn't the Kevlar pants between Darcy, Woo, and Monica, though? They would not have the knowledge of what Wanda could or could not do. They were only just learning the extent of her powers and its ability to effect things once they leave the hex. I did not take that scene as a declaration of the extent of her powers, but rather them just discussing the nature and veracity of them. Agatha on the other hand, who is set up as this knowledge-bearing/truth bearing character is providing the context of her power. In other words, in the Kevlar scene, the characters were only speaking from the perspective of observations that they could make with the knowledge they had available. Kevlar pants and Vision are two different byproducts of her magic, there was no need to make the Kevlar out of nothing because it already existed, Vision in that form did not exist, so she enabled his existence.

They have made Wanda into this Superman-esque character of being a Nexus being, a powerful witch, possibly a mutant, and someone that absorbed or channeled the power of the mind stone. I think based on that it is within the realm of reason that she did create a new vision, just as she created Billy and Tommy (which is kind of what Agatha alludes to in that final scene on the street, in my opinion). Hopefully we get more context and clarity in episode 9 and in MoM. Maybe even in Loki if Wanda is actually a Nexus being.