Why not a redundancy-lost message?
While considering system updates, how about the generation of a message something like:
pitot redundancy lost, review UAS procedures
before the autopilot dropped out.
I don't know how long before autopilot drop-out it could/would have been generated, but it would surely have reduced the startle factor.
My guess would be 10s of seconds from the rejection of the unfrozen pitot to the divergence in readings from the other two pitots leading to the declaration of UAS.