What I want to add is that the more realistic version of this vision would be to imagine a system not where a president can remake vast swaths of policy merely be decreeing it, but rather a system in which a unicameral legislature can remake vast swaths of policy through majority vote. Such very real, totally non-tyrannical places as Canada, the United Kingdom, the Netherlands, and many others operate in this way.In fact, however, the unicameral legislatures in most democracies (although there is a range, and I'm not at all an expert on where the various nations fall within that range) don't "remake vast swaths of policy." What they do is take whatever the government proposes, and ratify it. The governments (that is: the prime minister and the other ministers) are from the parliament, but not really of it. The big power retained by individual legislators on the majority side is simply to threaten to bring the government down altogether, not to actually draft and amend legislation. The United States, by contrast, has a "transformative" legislature, in which Members of Congress actively shape laws. We often think of this in terms of "veto points," and that's not wrong -- but it's also true that there are far more "initiation" points. For example, in the current banking bill, Al Franken's amendment on the ratings agencies was a serious, substantive addition to the Senate bill. It didn't come from the president, or from the Secretary of the Treasury; it came from a single Senator, and an extremely junior one at that. And of course now the bill is in conference, and I guess there's a compromise, all worked out by Members of Congress, with minimal input from what in Britain would be called the "government."
While the question of majority or supermajority rule is related to the extent to which legislatures are independent actors, it really is a different question. I really don't know much at all about the Unicam in Nebraska, but as far as I know it's as much of a transformative legislature as is the California or New York or Texas bicameral legislature.
And there are really good reasons to want to have that sort of arrangement. I wouldn't exactly call the British system "tyrannical," (although it does strike me as pretty goofy that the minority Conservatives have so few constraints on implementing their ideas), but I do think that the American system is far more open to meaningful participation by small and new groups of activists. And, while I'm not a big fan of majority rule on principle, in reality majoritarian systems generally provide, in my view, more of an illusion of majority rule than the real thing anyway -- because in reality, public opinion doesn't break down by political party very often, so the "in" party probably represents the majority on some issues, but the minority on others. At its worst, if the political parties are hierarchical and impermeable, I think a case could be made that these systems are not very democratic. On the other hand, the American system has its own problems, chief among them a likely (stronger?) bias in favor of the status quo. That's not necessarily all that democratic, either.
I guess I would say this: at their best, parliamentary systems are great at efficiently translating election results into policy. The inherent problem with that is that it gives elections a meaning that they generally cannot support. At its best, the American Madisonian system is great at encouraging participation and finding ways for millions of people to meaningfully participate in politics and government. The cost is a whole lot of frustration when election results are not rapidly translated into policy.