> That morass makes it difficult for the public to cleanly digest when something is blatantly unconstitutional
I'm not convinced that's a relevant issue here. For some parts of EU treaty law, sure, but here the context here is disapplying EU legislation that's incompatible with fundamental human rights. Those parts are all in one document in one treaty: the Charter of Fundamental Rights[0], which was incorporated into the Lisbon treaty.
(besides, whether in the EU, somewhere with a formal constitution like the US, or the UK, the vast majority of the work of figuring out whether something is in breach of treaty / constitutional provisions is always going to be analysing caselaw)
Admittedly, a narrow one: clearly delineating unconstitutional behaviour and allowing it to be called out.
> collection of member state treaties is for ~all intents and purposes a constitution, just not in a single document
That morass makes it difficult for the public to cleanly digest when something is blatantly unconstitutional. (Britain has a similar problem.)