Re: It's actually good.
Doctor Syntax,
One problem the US have is how politicised their judiciary has become. Or possibly has always been. I can remember complaints from the 90s about how the Supreme Court still had a Democrat majority despite there having been 3 Republican presidencies in a row. Too many US political issues become mired in arguments about arcane readings of a 300 year old document that often doesn't even mention the topic in question. At which point getting your judge onto the Supreme Court, where they might last 50 years might have more long-term effect than any law you pass. Although famously both parties have got their candidates into the Supremes only for them to consistently rule completely the opposite way to what was expected.
In the UK our judiciary is much freer from that kind of political interference. However there is a danger that it becomes part of the establishment. Obviously, what could be more establishment than being a judge, but you need your judges to be independent of the people who run large organisations and the civil service - or you risk ending up with a technocracy. Where if an elected government does stuff the establishment doesn't approve of it first gets slowed down by the civil service and then gets thwarted by the judiciary.
In the British Supreme Court judgement you cite about Johnson proroguing Parliament there is pretty good legal argument on both sides. The judiciary ruled in a novel way that intruded into an arcane area of the constitution that I'm not sure there was a great deal of basis for. Of course it was an unusual situation, and that's what happens in a precedent based constitution like ours. Sometimes judges effectively make new laws - but if Parliament doesn't like it, it can usually change it either back or to something else.
Similarly in the Gina Miller case, which ruled that Article 50 couldn't be passed without a vote of Parliament. Again the same "establishment view" won over the elected government. the court made a novel ruling for a novel situation. The constitution is clear that Parliament votes on UK laws and that the government does negotiation with foreign powers. Of course the ruling had a good point, that leaving the EU then changed a bunch of laws, because it's not a normal treaty. But here, the experts were all wrong. The government, Gina Miller's team both testified that Article 50 was irrevocable without a unanimous vote of all the EU members (that was also the European Commission's legal position) - and so the court ruled that since triggering A50 would de facto change domestic law, then Parliament should decide. It's a perfectly logical position. The ECJ later ruled that the UK could revoke A50 unilaterally. Which pretty much ignored the text of the treaty in question - again judges probably going further than they should - but I do wonder what the Supreme Court would have ruled had they known that? It might have changed the Parliamentary situation completely and had huge effects on the outcome of the constitutional crisis over Brexit.
I guess my point here is that judiciary needs to check the executive. But it needs to be careful. Too much judicial activism can make the courts so controversial the politicians are tempted to take drastic action, because they keep being hamstrung by people who lost the election but making an end-run to keep fighting in the courts. However historically a lot of our laws have stemmed out of judicial activism. A lot of early legislation on food standards stemmed from a court case about food poisoning setting a precendent and Parliament having to run to catch up - and broadly implementing the law as the judges had made it.
I guess the point of checks and balances is that it has to balance. Which means that the judiciary have to show utmost restraint, as they're not answerable to anybody once they've got the job. Which is dangerous power, that it can be very easy to abuse - even when you think you're acting for the best of reasons.
As for the House of Lords it still does a pretty good job. It was better when it was less democratic, becuase the ex politicians were even more out-voted by the old aristocracy and the people elevated for doing good works or generally being honoured for having been prominent for a long career. But most of the best work from the HoL has been in the committees anyway. Sometimes it delays legislation when the government gets too big for its boots - but a lot of good work is done by subject matter experts who get onto the committees and scrutinise legislation in detail. They often get their work taken up by the government and added to legislation, which increases the quality of our laws. This works less well in controversial areas though, where the government tends to try and fight off the amendments, although partly that might be because many of the amendments aren't trying to fix bad draughting, but trying to change the meaning.