Yes! When I see US jurisprudence getting tied up in knots about whether given rules 'are jurisdictional' or 'are merely mandatory' I can really see the benefit

Yes! When I see US jurisprudence getting tied up in knots about whether given rules 'are jurisdictional' or 'are merely mandatory' I can really see the benefit of the decision the HoL took in Anisminic. And it does permanently prevent flagrant abuse of judicial power by lower court judges. But the legal fiction of parliamentary sovereignty does feel a little more fictional when you read that case. (Of course, they were careful to make clear that Parliament was, in fact, still sovereign, and given a sufficiently expressed will, etc. etc. But in practice...)