This is a game of ever changing politics and deals and diplomacy. Nowadays, people seem to think every kingdom has the right to fight 1 on 1 wars. When the game started, people could fight in 2 wars simutaneously and it was not considered unfair.
There's no need for the developers or mods to determine what sort of deals kingdoms should be able to make in fighting, the utopian community polices that sort of thing well enough. And the policing and determining what is right and wrong is more often the most entertaining and fun part about the game.
Any developer or mod stepping in in this situation is overstepping their bounds. If they do not like large provinces gaining off of small ones, simply change the rules next age to make the in-war landgain system similar to the out-of-war landgain system. Out of war Ryan would only gain 3 acres per hit. Making such changes is in the developer/mods power.
Or even better, why not just change the whole system for the better by implementing the following changes:
1) Make the explore formula more exponential, so that one province can't take a majority of the kingdoms explore pool
2) Make explore pool not go away in war, so kingdoms can re-grow chained provinces after war so kingdoms who war aren't "screwed" by having really small provinces for their next fight.
3) Then you can eliminate all EoW/Fortified doubling of explore costs.
Have the explore pool serve a real function: To not penalize kingdoms for going to war, and to let provinces recover after wards. Right now the explore pool is pretty much solely used by kingdoms and provinces that wish to rank higher.