I could be wrong here, but it sounds like you keep looking at this essay in terms of "what" - as in "what institutions of the legal system support / limit power of judges", and so far you have only come up with Parliamentary Sovereignty. Ok. But that's not how I would approach this essay. I read it as taking the last bit much more weightily. "...especially in cases where there are compelling reasons to do so."
So my train of thought is - start with a case where there were compelling reasons to change the law. Look at cases where the law has been changed (like Ivey) and also cases where you feel that the law is quite old. R v Brown isn't a bad place to look. There should be quite a bit of academic writing on Brown.
Then ask yourself - did the law need changing? Was it changed? In the case of Ivey, yes it was, and in a way that has quite an important bearing on a lot of future cases. So now look at how the common law and how the system supported that change and why statute wasn't used. Then apply the same rationale to your counter case. Is the reason the law hasn't changed because of our common law system, is there something stopping / preventing that change? This approach looks at what has happened and how - rather than trying to name institutions.