Big clans have manpower and infinite resources to just keep building/blocking every part of the map on official servers. By accumulating explosives they will forever just hunt down the smaller clans and keep their dominance.
One way to nerf alpha clans would be increasing building costs based on how much you build. If you have a big base, producing construction elements should cost more. This way, smaller clans have a way to “get into the game” because of lower production costs. When a player joins a clan, all their buildings should be lost to avoid exploiting this system.
This would be less limiting than an upkeep system: you can still build as much as you want, but the grind is harder.