I think the added flight range of the Su-33 would be useful in some situations, so having a couple of them on board as well as their main aircraft the MiG-29KR would be useful.
Remember the MiG is in two and single seat models so it effectively replaces some Su-33s in the fighter role, but eliminates the Su-25 in the training role.
Note the carrier based Su-25s did not have weapon pylons and were not armed so they were only landing and takeoff training aircraft.
They might have been able to carry aerial targets in a target towing system too but the MiGs could do that as well.
They already said the Su-33s had upgrades to allow high altitude bombing with decent accuracy to be performed which would require significant upgrades to an aircraft that was essentially an Su-27 with no ground mapping/targeting capacity...