Basara's appearance in battle as pointed out "was" a planned action. Project-M was initiated by Max. He gathered Chiba, Ray, Basara, Akusho, & the VF19 Kai into place knowing full well that Basara would go out into battle and sing. Basara didn't happen into the cockpit, he didn't steal his Valkyrie, it was custom designed "for" him, and Ray had several years to teach him how to fly it. That is no less a sanctioned military act than Minmay's singing, and is much more than Ranka & Sheryl's.
Besides which, Bsara had pinpoint barriers, "if" he got inbetween Varuta firing on a pilot, and a pilot firing on Varuta, it's tot he pilot's benefit.
And there's your own defeat to the claim that Basara has no growth arc TY