It still had to be respec'd, Kou only had the ground type core fighter to work with, they lost the other one during gato's first raid, when they had to shoot down the spy escaping in it. And the one they had left had to be revamped into FB. Simply swapping core fighters was no longer and option, and why Kou was head strong about his calculations because it's pretty much the word of the pilot whose gonna be actually operating it against the word of the person who made the gundam with expected parameters but has never tested themselves, again it's that whole practice and paper thing being shown. Kou still fucked up sure, but that still him getting humble and learning better cooperation.