When I saw your user name appear as the newest registered member I thought "bet that's coming my way"!
Strong maths is definitely a point worth raising, regardless of the effect on VR skills! However, I know from my own experience that children (especially boys) who are strong in Maths, Science and ICT tend to find VR more difficult than those who excel at English.
For my own son's appeal 2 years ago I did find some evidence on the internet that children who have dyscalculia (poor at maths) will tend to have higher VR skills than the average. Unfortunately it was a quick mention on a special needs website and did not really constitute solid proof of the issue.
Despite that, I think a panel will accept "strong maths = possible weakness in VR" as a secondary argument - "worth a mention", as Etienne would say.
Our son scored 118/119 on the Bucks VR tests, which was a big surprise to just about everyone, with him having been predicted to be a safe pass. We have no mitigating circumstances to quote and can only put his not passing down to a blip. His year 5 report scores were 5c, 5b, 5b and he is ranked 8th by his HT.
Another surprise to us was that this year his school has only a 16% pass rate, which I think is pretty poor.
Do you know what happened to the 7 children ranked above him? If they all passed and preferably a few below him passed as well, then it will help your case, as he will stand out as a "blip". You will receive a copy of the Order of Suitability with your appeal papers, so if you don't know the answer now, you soon will.
That is the context in which the school's poor pass rate will have to be examined. Otherwise, as you say, it is a tricky issue to raise.