I have seen solo flights sent when either the conditions were less than ideal, or the subject themselves were close to the limit of their ability.
Which was it - Operating with no supervision or the supervising instructor not doing any supervision?
The Restricted FI is learning how to do the job. They need to receive appropriate training and be given the opportunity to practice what they learn. Even if they are part time, if they do not get the opportunity to supervise solo flights then they are being let down by the person / organisation that has agreed to give them "on the job training".
Failings in the JAR-FCL system are simply a result of the people involved - The CAA, Training Providers and Supervising Instructors intentionally running the system in the least safe manner to make a political point.
The old UK system - 200 hours of exercise 3 and an easy course and off to teach instrument flying at their own school with all of 20 hours instrument flying (under the hood) in the logbook. Love it.
Likewise it's perfectly OK for the student to do 3 circuits, come in for a coffee, go again = 3 x 20 min circuit trips in a day, earning the FI(R) 3 sign offs rather than 1 sign off from a hour trips!
An upgrade test would be far more useful.
As I have pointed out. The restricted FI can do what you describe 5 days a week for 6 months and they will only get a recomendation when they have demonstrated the required standard in all areas.
On observing the above I would simply ask to sit in on the de-briefing and the briefing for the next flight. There may be a valid reason for having the student stop and come in for a chat.
Perhaps you could expand on how you think a test would be more usefull and just what problem it cures?