This is a perennial problem.
I seem to recall seeing a document at UAS HQ ( along time ago) that was produced to consider the usefulness of UASs, university cadetships and the recruiting of ex VR UAS studes (who had taken CBAT). It also looked at UAS reports and BFT docs over a 10 year period. This was in the day when OASC candidates had to have exceptionally high CBAT scores to be considered for GDP.
The report said that (as intimated above) CBT scores only 'indicated the potential of a candidate to pass BFT' (JP/Tucano in those days). IIRC the report quoted that the OASC CBAT score cut-off equated to a 60% chance of passing out from BFT. Not a bad filter.
However, the report also claimed that a candidate from the UAS VR pool who was assessed as High Average or better (CBAT or not - there were some from earlier days) stood an 80% chance of getting to a front-line sqn cockpit (it might even have been a FJ sqn). So, UASs were thought to be an even better indicator than aptitude testing alone and this was why the UASs system had a stay of execution in the late 1990s/2000s.
Nice tho' that was, I had a number of students who were high/above average but didn't get the required CBAT score at OASC and were either offered GDN, ground branch, or nowt. Often, these guys and girls were as good as (if not better in some cases) than those who were on cadetships. The latter were generally top-drawer too but they had the CBAT scores and a lot did very well. But it seemed daft to me that good people (who were well motivated and could actually fly properly) were not utilised. It was claimed at the time by some people at OASC that UASs were biased and their reports could not be trusted and it was galling to learn that the assessments of professional UAS QFIs (often vastly experienced) were often discounted in favour of CBAT alone. I believe this changed slightly after the general dissatisfaction of the QFIs and COs filtered up (and whose assessments were then taken as the 'gospel truth' once streaming was done on based on our reports!).
From our UAS alone around that time - most who joined ended up on FJs and QWIs/QFIs themselves and 4 studes (all VRs initially) even ended up on the Reds (long gone from there before the current hiatus). Other studes of ours (cadetship types too) have been Sqn Cdrs, Flt Cdrs, QWIs QFIs, IREs and TPs - even some of Air Rank. Almost all of those whom we sent to OASC (not all went) and didn't get the required aptitude scores have excelled too - airline training capts and CEOs of big businesses. Other UASs of that era will have a similar story of success and believe that system was the jewel in the crown of fg trg system. Bottom line - CBAT is fine as a first filter but back then, the UAS flying training system was a far better indicator, while the QFIs were professional instructors who knew better than any computer game the potential of a student pilot. Sadly, it seems we can't afford that anymore. That is not to say that the present streamlined system doesn't work; it certainly seems to from the guys and girls I meet around the bazaars. Today's fg trg system appears to get more out of everyone and very few of those who get good initial results are discarded. Back then, there were more of us and you were always 'only 3 trips from the chop and the bus home', which happened quite often - probably too often. So that is notable progress - today's best are still the best.