TBH. The solution here is simple.
Hold back on XP.
If they wonder why their characters take ages to improve and can never afford their promotions... Then point out that they are simply doing this themselves... After all, the experience and kudos is constantly going to the senior officers who do the work.
Have an NPC come on board and overtake them due to his can-do attitude...
DanG/Darth Gurden
The Voice of Reason and Sith Lord
“Putting the FUNK! back into Dysfunctional!”
Coming soon. The USS Ganymede NCC-80107
"Ad astrae per scientia" (To the stars through knowledge)