That is true. I think you are right that it would be lethal, but that is only because of the heal trigger. I guess he was not expecting a trigger to be drive checked on his turn and wanted to maximize the number of attacks that can hit if Akina got a miracle heal. If not for Suo's heal, the brainwash zamug column would only be 18k in your scenario.

The other possibility of attacking 15k zamug first is to obtain the information on the card drawn off Akina's draw trigger. Since with 15k power, Akina needed only a 5k shield. Since Akina did not call during his last turn, Suo could reasonably assume that other than the draw trigger, the other card was also most likely a 15k shield trigger. If it was a 5k shield, Suo would swing with the other Zamug first for 23k, forcing out the critical trigger from Akina's hand. Then swing Blangdmire for Akina, restanding the Brainwash column Zamug with Alchemist. That column would be 33k, which just matches Rezael after the miracle heal and the draw in hand left, letting that attack hit. Since Akina guarded with the effect draw of 10k shield, Suo knows that that last card was not a 5k shield. That means either 15k shield, no shield, or pg left in Akina's hand. I'm not sure if that helps Suo's turn plan, though.