That's actually really busy for a one track station. Of course you can't have 28tph with one track because it wouldn't be possible unless the one track section is very short in length.Lime Street Lower Level is as busy but it has 14tph from one track and one platform so it doesn't meet your requirement.
Down platform at Queenstown Road sees ~22tph (mixture of stopping and non-stopping trains) in the busiest hour in the morning contra-peak.
Up platform currently around 16tph in busiest hour
Liverpool James street has 28 trains per hour using 2 platforms (third platform only used if there is any disruption)
Chelmsford must be up there during the peaks
Not if we use the OP rules of the train having to stop though? Seems around 14-16tph to me?
Canada Water? 33 departures booked in the next hour
In terms of passenger numbers I believe it is Chelmsford, to add another dimension to things