There are plenty of problems with poor mechanical sympathy. To take an extreme example, traversing graphs is notorious. Cray and Sun iirc have some fascinatin

There are plenty of problems with poor mechanical sympathy. To take an extreme example, traversing graphs is notorious. Cray and Sun iirc have some fascinating processors with many many hyperthreads because all the programs do is wait on dram but luckily there are lots of searches that can be done in parallel.