It was mostly the idea that you could pull together an international treaty/agreement between over a hundred countries within, what, five days? No, that clearly would have had to be in the works for at least six months, probably more like a couple years, in which case its existence should not have taken ANYONE remotely by surprise. And if the negotiation of the Accords was known (and there really is no way that could have been kept secret), then the Avengers should have been lobbying for changes all through the process, and again, should not have been taken by surprise by anything other than Tony's sudden choice to support them after his previous very vocal resistance to being regulated by the US government.

The content of the Accords is more easily handwaved, as your speculations show.

But the timing/secrecy problem is even worse than the implication that it took less than a week from Bucky's fall to Steve crashing the plane back during WWII, though at least that impossible timeframe was not directly stated in canon and can therefore be handwaved as the film skipping over a bunch of bureaucratic infighting and other missions in order to focus on more arc-relevant scenes.