Higher density means more data per track, not just more tracks per disk. You get an entire track per revolution so a track with more data is more MBps. So linear reads on a higher density drive are faster, and semi-linear accesses (ie, reading two files that are next to each other) do get faster.
I remember reading a story about a guy who built a drive array with high capacity 7200 RPM drives that got within 20% of the performance of the 10K RPM setup they had, by partitioning the drives at the same capacity as the 10K equivalent. The head only had half as many tracks to traverse, so worst case access time was better, and the higher density made up for the lower RPMs.
Short stroking helps get more performance from the disk, at least in terms of latency. The bandwidth change occurs because the density is fixed and there are more blocks on the outer rings per track compared to the inner rings so in one revolution you can read more tracks and you don't need to change tracks so often.
You parent comment is right though, there are only small changes in bit density on the track in recent years so the bandwidth is not improving by much.
Higher density means more data per track, not just more tracks per disk. You get an entire track per revolution so a track with more data is more MBps. So linear reads on a higher density drive are faster, and semi-linear accesses (ie, reading two files that are next to each other) do get faster.
I remember reading a story about a guy who built a drive array with high capacity 7200 RPM drives that got within 20% of the performance of the 10K RPM setup they had, by partitioning the drives at the same capacity as the 10K equivalent. The head only had half as many tracks to traverse, so worst case access time was better, and the higher density made up for the lower RPMs.