That is undoubtedly true,and illustrates the problem of not having a legal system independent of government and non partisan. It also requires a constitution which is capable of being amended. The problems in the USA are stemming from these reasons. The problem in the UK might be that it has no Constitution... Just a set of frumpy conventions. Which are now being flaunted.Its the modern way since Bannon realised the massive loophole in the states.
Cummins is just following along.
I could see the UK Supreme Court agreeing that the prorogration was illegal because it was not a decision of parliament,..that would not be a party political stance, as it would be again reaffirming the supremacy of Parliament,not the Executive.