I find Percy’s comment to Vax about the children “finally finding out how much [he’s] embellishing the memory of you,” while a very Percy quip, to be so telling about Vox Machina’s collective denial about Vax.
Because it’s meant as a quip, a jab like they used to do, the implication being Vax hasn’t changed. But Vax doesn’t react. He has changed. He is not 100% Vax anymore.
None of them, not Vex not Keyleth not Percy, are having a normal conversation with him like old times and talking to the person they knew. But they’re pretending they are. They are clinging to the thing Percy is actively embellishing as the Champion stands in front of him: the memory of Vax.