Trying to have a normal conversation, can you stop with the silly baseless attacks because you happened to misinterpret a scene? It's really not a big deal; I'm not making it one.
They overloaded the machine, the resulting explosion (ie machine exploding like a bomb) destroyed the landmass, this was literally the plot. Giving Thor and/or Tony the ability/feat to destroy a city because they used something else to do so is flawed; it's not like this ability is standard to either of them. You're giving Thor and possibly Tony feats they do not normally show/possess.
(This is an aside as it really doesn't matter to our convo, but the landmass wasn't going to free fall, the machine was going to reverse polarity and then speed the landmass back down, turning it into a humanity killer. Tony explains this as well in the scene)
edit: Look at it this way, do you think Thor could destroy a landmass as we saw without using Ulron's exploding machine?