That's because scrypt is using the wrong memory hardness. The really hard problem in reality is memory load latency (assuming a large memory with random access

That's because scrypt is using the wrong memory hardness. The really hard problem in reality is memory load latency (assuming a large memory with random access). We essentially haven't made much progress on that font in decade(s), but have tapered over it with ever increasing levels of cache. If the access is effectively random, then the caches won't help. Base the crypto on that!