1.- The 32% gap between the HP pools of players changing the HP flag.
2.- The real advantage of combat that is 15%.
I can't beleive you are still going on about this. The real advantage in combat (against a deimigod that lost the flag) is 32%, same as the hp relation swing on the exchange of the flag ownership. There is (almost) never a sitation where the state of gaining the flag is not simultaneous with the state of losing the flag. Pretty much same as Erebus bite, one loses one gains. This is a constant state change, even if they disengage, the next time they meet they are still at this state where one lost and one gained.
Noone argues that your personal buff is 15% and if you compare against creeps, minions or towers that is the combat advantage you personaly gain as they never had the flag and their state has never changed. However, against the opposing demigods which lost the flag, the state changed by 32% offering you that much advanatage. Only the initial state change from neutral gives someone 15% advantage, all subsequent give 32% becuase one loses and one gains. As I showed in my TB/Oak example, absolute hp numbers mean nothing the state change may or may not put you above opponents hp and absolute strength.
The problem is that you keep looking at absolute numbers - like the (only working for your case) equal hp example that you keep insisting on. However there is no absolute relation of a single parameter (like hp) in the game, only a difference in the state before (A has, B doesnt have the flag) and state after (reverse).
Or to paraphrase, using the numbers you insist on.
A 2000 hp, 100 dps
B 2000 hp, ~86,95 dps (15% less)
1) no flag owner, both have 2k hp, A has base 15% advantage
A kills B with 261 hp left
2) A owns flag, A gains 2,3k hp, A has exactly 32,25% advantage
A kills B with 561 hp left
3) flag changes ownership, A back to 2k, B gains 2,3k hp, A has 0% advantage
The state change 2 -> 3 made exactly 32,25% ADVANTAGE for B (or reduced A's advantage by 32,25%), just cause of the flag changing ownership, no other parameter was changed between the two directly adjacent states. It doesn't matter at all that both never changed hp by more than 15%.
You can only observe advantage between adjacent state changes as that is the only state change that occurs in the game. Observing it between arbitrary changes (like 1 -> 3) is irrelevant.
EDIT: Cleaned up for clarity