Could the rival guy be used for those past GbG championship buildings? It’ll be challenging for certain to create an hard, yet fairly balanced GbG-rival line.
For example after completion pushing attrition to 100 but being beatable with 1 GbG building. Quests could be centred around making advancements, donating goods, winning battles or negotiations (always give that alternative as not everyone is a fighter). Do not include requirements like dealing the final blow to take a province in GbG. As this will cause internal friction within guilds. Potentially requiring to beat GE1, GE2, GE3 and GE4. It’s maybe possible to give for the final quest the option to either bear GE5 or hit 100 attrition or X-advancements.
The rival could be used to revive old GbG buildings. Giving the opportunity to complete old GbG championship buildings by handing out fragments to complete them. At most for completion just 1 selection kit worth of fragments upon full completion of the GbG-rival quests. So, those who ain’t in diamond don’t get a shot at lvl2. While those who didn’t manage to complete lvl2 during a past championship get an 2nd time to do so or a chance to complete the base building w/o the need to fully beat the rival.