I'd be very careful when I use the word 'stable' when it comes to the U.K. This is , in case you didn't know, a democracy that has had a 'Conservative Party in charge for more than fifty years since World War II ended, has elected as its leader for eleven years a minister so conservative she makes Reagan look like a softy in some ways and in the last fourteen years has endured both austerity and Brexit. They may not have a cONSTITUTION but the U.K. doesn't have much of a country left either.
Right now in a desperate attempt to shore up votes in what will be a routing by his party Rishi Sunak has been working on 'The Rwanda Plan' a plan to take immigrants and ship them to one of the worst human rights violaors in the world. This plan was eventually ruled illegal by Britain's Supreme Court so Sunak just had his government move Rwanda to the category of Safe countries in what is a legal fiction. Throw in the fact they've had four different prime ministers in less than five years (one of whom lasted less than a head of lettuce) and you really might want to rethink your model
Right now I really think BrtiaIN NEEDds a constitution. There may not be tyranny in the United Kingdom but there sure as hell is chaos.
The fault is not sadly with the Consitution but with those who think it should be interpreted exactly like it was in 1787. Unfortunately that now includes the Republican Party. And no its not the Supreme Court: their interpretation never even fits the models of originalism they claim it does. I honestly believe that for justices like Alito and Thomas they've made up their minds how they're going to rule before the arguments are made, have their opinions pre-written and simply fill in the statements they made like Mad Libs.
And I'll be honest. I don't think amending the Constitution SHOULD be easy. Do I think we should be following the standards of 18th century america? No. I also don't think it should be done along the level of a reality show which sadly sounds perilously close to what your proposing in one of your suggestions. And since one branch of the Democratic Party believes you should be able to change it every finve minues, I'm not comfortable with letting them have the say either.
Of course the constitution can't adjust to modern realities. But not because its was written 240 years ago. Its because the world can adjust to today's realities. In my lifetime of forty-five years technology is different in ways I couldn't have pictured forty years ago? What system of government could possibly hope to stand up to that benchmark much less one of two hundred years ago. Forty years ago, we were still basically denying that gay people even existed in our society and that Transgender people did either. No woman had served on the Supreme court in its existence and the first African-American named was still on it. No woman had launched a serious campaign for President and the idea of an African-American getting the nomination, much less winning the White House was the stuff not even a TV series would consider realistic.
America has spent too much of its history moving forward slowly and taking as many steps backwards as it did forward. Society has never moved as fast as many in America have wanted it too. It's made up an enormous amount of ground in the last sixty years - more than most on the left want to admit, too much for those on the right - but its direction has always been moving just fast enough.; We have too many problems in today's society but they will never be solved by burning things down. Our problemm isn't that the constitution can't adjust to modern reality as you say in your last sentence. It's that reality changes so frequently., no one and nothing has chance to keep pace. Honestly it would be simpler to get the rest of the world to adjust to reality before changing the Constitution.;