There is no problem about farming neither about arty. Problem is that HE arty should destroy the whole farm in 20 seconds (imho also HML tank should do that but in a little longer). So if we should change anything the thing is damage done to turrets by vehicles.
That's just one. Choose wisely. The basis behind that number is that you should have to work harder to defend refineries, primarily because they're extremely important structures that deserve your attention. Also, it means that any defense of a built and abandoned refinery isn't going to hold for very long. IMO it would encourage either fortification of and/or fighting over a resource node.
Millions of turrets causes lag, eats all your FPS and, as said, effectively places the game at a standstill. It doesn't matter how 1337 you are, you still can't bypass a turret field without laboriously destroying every single turret (well, in 1.05, when you can't trick the turrets by crouching) - which easily gets extremely boring without a couple of artillery tanks. More open space for mobile tank battles would be better.
turret farms are boring indeed. make the game less about static defenses if possible. atleast make the other team suffer more if they are TOO defensive.
