Eh, that doesn't math out. It's the bandwidth per storage density (or ultimately per price) that matters.
If you have great cost per byte but your bandwidth per byte is bad enough that the price per byte doesn't make up for it then you have an issue.
They've started making hard drives with multiple heads because of this issue, they increased density to the point where it's not useful to continue adding density if it doesn't come with more bandwdith.
Yes it causes problems in this increasingly narrow situation.
Massive storage that takes a month to fully read is acceptable in a wide variety of use cases. If it's cheaper than hard drives it'll get a huge amount of users.
Interesting, this is my first time consciously thinking about this trend.
Perhaps the needs for read/write speed are bounded (before processor, etc. becomes the limiting factor), while more capacity is only limited by price. Or maybe increasing density of storage inherently means a tradeoff with I/O speed (AFAIK, NAND flash needs to rewrite lots of data just to make a single write? Atom-scale interactions have side effects)
To be fair, if I'm reading an exabyte in a month, my hardware's pushing >3 Tbps, which I'd be very happy with.