That only works if both readers issue requests without waiting for results. That's not how programms usually work - if they issue a read request, they wait for it to succeed before sending the next read.
Anyway, if you have such workloads and you do *not* pause, what happens? You perform the first seek to A, read, A, seek to B, read B and in the meantime, more requests for A have arrived. If it's only one, you still seem to be fast enough despite seeking - just seek back to A and go on. If the seek takes too long, multiple request should have been queued already and you can coalesque them and handle them with one seek.
IMHO, letting a disk stay idle when there's work to do is wrong!