So the top guilds currently have a monopoly over the towers by owning them 24/7 without ever losing them. This can be solved not by hindering their ability to hold them, but by adding more. I think at least 5 more towers should be added to the map. Perhaps make 1 or 2 KOTH to please those who liked it as well as add to the ways to take towers. Start with 1 or 2 and keep adding more until it's possible for 4-6 people to take a tower.
The only problem is having multiple towers across the map without creating new areas would spam the map with pictures. New areas with shops and stuff could be added for room for towers. There is room in belle isle, north Graal city, and Onnet for towers.