This may seem a bit unconventional but bear with me. What if the only way to get TNT was in small increments of a few TNT only, from airdrops/mcmmo/supply drops/KOTH/etc? One chunk of walls would be about 8 walls. Most cannons need about 800ish for a simple fusion to get through one wall, so about 6400 TNT or a dub and a half of TNT. If TNT was available only in limited amounts, raids would still happen and would be a bigger deal whenever you get the TNT for one. To be able to raid your faction would need to actively participate in server events. Smaller factions would not be raided as much as people would reserve their TNT for richer raids. You'd lose more power if you died in a chunk where TNT has recently been detonated so raiding dynamics could be even more exciting. Really just rattling off some ideas that could be fine tuned pretty well, but I think it sounds like a really fun concept reminiscent of the way factions used to be played.