I see what you mean but I didn't feel that. I mean, the stormtrooper thing, yes. That's what they were made for, to defeat them on a greater scale in a big battle such a movie demands. But I don't think the tension was supposed to come from that. The tension worked for me through the characters, Ultron's plan and the knowledge that Whedon would kill off an Avenger (which I feared to be Hawkeye after the set-up with his wive and kids). The showdown was more about saving people anyhow, which I found very refreshing after the Man of Steel destroyed dozens of skyscrapers when he battled General Zod.