Military Aircrew aptitude tests are hard, but they are bound to be, they are designed to filter out the less able.
Lets just put this into the correct perspective. By
less able I hope you agree it means less able to cope with the rather specific requirements to train someone to be a military pilot.
The military look for a very distinct product. Not fitting into that category does not, by any means, suggest that a person who does not pass OASC selection is not fully able to excel in another field, even civilian aviation, it just means they are not what the military are looking for.