Please find below my proposal:
1) Battle won implies some material i.e. some supplies for the winner
2) Encirclement and destroying implies
2.1) for the winner some material i.e. some supplies + some leadership increase (you likely captured some leaders)
2.2) for the looser some leadership reduction
3) Annex a country implies for the winner some material i.e. supplies, depots, IC, etc + some leadership increase (you likely captured many leaders)
Please let me know your thoughts
1 - Fine
2.1 - No. Perhaps during Annexation, Puppeting a leaders may be willing but too often military leaders would simply be executed or jailed.
2.2 - You lose the officers and I'm sure you'll already lose some leadership based on DDs.
3) You already gain all money, supplies, materials, IC. Leadership should be very minimal due to reasons I've outlined. I'd simply rather that you gain some theoretical research in areas that you're weaker in.