I think the chop was valid. What you failed for was two things. One was choice of the wrong safety altitude. You should brief the safest and then look for ways to reduce your altitude safely from the MSA.
The other reason was for a compensatory failure. In other words your initial failure was fuel handling. On the next flight you ensured that that failure did not reoccur but another 'failure' became apparent.
It is all a question of juggling and priorities. You dropped two different balls on successive trips. How well had you passed your earlier exercises. When I was at the ANS we were also surprised that one of our studes was also chopped from the advanced multi-engine phase on his final sortie.
I had a stude who fell to pieces completely in the air and wanted to RTB shortly after TOC. I kicked him around the route and failed him when he landed but . . .
He was SAFE. He did not overshoot his Stornoway turn nor did he bust safety altitude. Last I heard he was a GR1 flt cdr.
In the final analysis there is always the question of what if.