Why is MySQL Workbench is reporting different number of writes per second at the same time on the same database?
Perhaps that figure is a snapshot with a tight granularity, reading the number of writes once then again after some portion of a second, and multiplying up to get a "per second" value. In that case I would expect the figures to differ every time unless you somehow request an update of both at exactly the same fraction of a second.

If the figure is an average taken over a larger timeframe (multiple seconds instead of one or a fraction there-of) then the figures would be closer to each other.

You can see a similar effect looking at CPU use on any unix-a-like system by running two copies of a top variant in separate terminals. The same for disk and network IO with iotop and iftop or equivalents. They will almost always show slightly different figures as they poll for updated data at slightly different times, especially if you turn the update frequency as fast as you can read.