The new franchise plan of 2016 called for 21 185s to leave the fleet. These are being retained
However, this is partially cancelled out by the fact that the Cleethorpes service has been extended to Liverpool (4 extra sets), the Huddersfield stopper is being extended to York (2 extra sets, assuming single units) and the Redcar service has been extended to Saltburn (2 extra sets).
The Hull service has also been extended to Liverpool (4 extra sets) in lieu of the Scarborough service which was (mainly) Mk5s, although it's uncertain whether this will return after the December cutback.
I don't have the details of the original plan to hand, but it might also have assumed some all-day single sets on Redcar/Hull/Cleethorpes, each of which
should now be doubles, at least in theory.
plus the 802s aren't being heavily utilised at the moment
Not 100%, but the availability has never been as good as promised/assumed (GW and other TOCs who are pushing their 80x fleets hard are suffering from this). There's also one set which is still accident damaged following the Heaton derailment, and another which is (or was) out of service for battery conversion testing.
Unless the former Newcastle-Manchester Airport/Piccadilly service group is totally withdrawn in future, there won't be a lot of spare sets to cover for the withdrawn Mk5 sets. The net effect will be a loss of capacity.