Superman's flying fight doesn't result in much building smashing in Superman II, due to technical effects limitations of the time, which renders their blows pretty weak sauce, but also the concern for supersonic wrecking balls tearing down buildings moot. Superman mostly punches them into billboards or walls which only dent. Not through the wall, the wall behind it, out the other side of the building, into the next building and two buildings behind that. You can argue that if they were able to make those shots in 78, they would have made them. But we have to go with what's presented on screen. Granted, Supes does punch Non out of the ground and actually all the way through the Daily Planet. But that happens once, not every time. And his hand hurts after doing it, so he probably gave it his all for that punch. While in Man of Steel, it seems effortless for them to throw punches like that. So the power levels at display are wildly different. It is conceivable for Superman to be able to fight them without risking tearing through countless bedrooms with the power levels at display in Superman II, as long as he sticks to rooftops. It might be dangerous and irresponsible for Reeve to take them on in Metropolis in Superman II, but nowhere near as dangerous as it would be for Cavill's Superman. Plus, in Superman II, the people that Zod and gang target are standing in the street to watch the fight instead of getting the hell out of there, so they pretty much have it coming.