Not gonna work:
1. They've shown that they're willing to outspend their rivals, saving up won't help you
2. They've got massive stats, and will keep growing while you save
3. They've got all the mods stacking up against you while you save
4. They are willing to outspend you coz they're defending their unbeaten run
Only way to break this is if the game mechanics change and :
1. allow MW style destruction of units when fighting. Then put together an alliance to hit fc members and run their units down. It'll be a massive war of attrition. Alliances will be tested and it'll be quite an orgy.
2. Change mods to expire after a period of say... 1-2 wars.
Even if the leaderboard doesn't change, the drama from the fighting would be entertaining