It's called tact and how to use it. Is brute force the BEST methodology to destroy or fight Ultron? Probably not, unless utilized on the right spots or in a specific point. Does that mean he is invincible? No, as I've stated before, even outside of Marvel and Comic type stuff, I've lost AS Ultron despite all that durability. They were hard lost matches, of course, but its FAR from being impossible and from what I've seen here, if it isnt physical force it'll be something else.