>We see PMs easily enacting massive legislative reforms and even Constitutional changes that are nigh impossible in the US
I don't know about UK but in Australia we need a Referendum (https://en.wikipedia.org/wiki/Referendums_in_Australia) to change the constitution and those have been historically extremely difficult to pass (only 8/45). The PM absolutely cannot alter the Constitution.
Yeah, it’s dangerous to generalize parliamentary systems too broadly. That isn’t the case in all of them. But as you can see in his comments, he thinks that having “constitutional” laws above other laws is also a bad idea.
I don't know about UK but in Australia we need a Referendum (https://en.wikipedia.org/wiki/Referendums_in_Australia) to change the constitution and those have been historically extremely difficult to pass (only 8/45). The PM absolutely cannot alter the Constitution.