Two captured Imperial Space Battleships were not sent back to Base Five for repairs. Instead, they were fixed by the brave Federation Mech Repair Soldiers amidst constant threats of attacks from the Imperial Fleet.
There's not much difference in skill level between Mechanics and Mech Repair Soldiers; it's just that the former usually stay at safe bases for repair work, while the latter must remain on dangerous battlefields throughout the year.
In this respect, Ji Xinghe could now be considered a Mech Repair Soldier, albeit a Major General-ranked one.
The repair operation had to be carried out away from Base Five because no one could guarantee whether there were lethal threats onboard the battleships that could pose a fatal danger to the base.
For instance, nuclear weapons hidden within the armor layers would of course, represent the worst-case scenario for the Federation.