This is simply wrong. The Supreme Court found there was no justification advanced at all by the govt (not an irrational one) for the length of the prorogation. 
Whet the govt really mean here (notwithstanding the reported misunderstanding - which, by the way, I doubt is really a misunderstanding) is that they don’t like the proportionality review which has arrived through EU and human rights law.
However, reality is ‘wednesbury unreasonableness’ (high bar, no reasonable decision maker could have reached decision) still applied in admin court cases every day. Proportionality review (could less intrusive measure have been used?) still mostly limited to human rights cases
What is *really* going on is that the govt know that with large majority it can do what it likes in Parliament but courts may still get in the way to apply pesky human rights and rationality standards ensuring govt acts within law.
That’s separation and balance of powers and needed more not less because of powerful govt and expansive executive (see Cummings blog - this is govt which will be run by executive). Absolutely essential that any ‘technical’ sounding court reforms are fought hard
Having said that, I think I did comment at the time that I thought the prorogation decision felt quite proportionality-a-like - this is not a bad thing! Proportionality is a useful standard for assessing interference with rights.
