The KBIT-2 is considered a screener, rather than a comprehensive instrument. There are differences of opinion in the professional community regarding how comprehensive the RIAS-2 is. (I assume this was a RIAS-2, and not the now-outdated RIAS.) Requesting a more complete assessment would not be unwarranted.
FWIW, there is some research suggesting that the RIAS nonverbal composite, in particular, diverges somewhat from some of the other standard instruments, with not particularly strong loading onto either general intelligence or nonverbal factors. Speed (if this is the RIAS-2) is probably not the main issue, as some attempt was made in the revision to reduce the impact of speed. It would not be shocking if a WISC-V came up with stronger Fluid Reasoning scores than the RIAS, given the student's KBIT-2 scores.
