I feel almost certain now that Maeda probably corrected/redrew most or all of the mechanical portions of this scene. While the character work & FX work could still be Oshiyama, there is simply no way he could have drawn mecha work of this quality so early into his career.

This would have required a specialist's touch, and Maeda being the Mecha AD & having decades of experience in his role absolutely fits the bill.

The only other alternatives would have been Habara, who is at the bottom of the KA list, and Matsumura who at the time would have been far too in-experienced.

Sadazaki is also possible, but their mecha work is highly underdocumented,