Stoppers, the reason is more likely to be as the result of the delay in Arsescent being able to meet the RAF's requirements.
One wonders who will pick up the tab for the L3 interim solution?
As for 40% of the Phenom fleet now being unavailable, one also has to wonder what the heck happened if both aircraft became 'poorly' on the same sortie....
Regarding other airframes, I do wonder why the Jayhawk wasn't proposed - a civil design specifically modified for the military training role.