You could say "Yeah, but what if the map only has choke point?" but that just means the map is balanced in favor of turtles
I would go so far to say it's a bad map. 3-4 choke points make for interesting games.
As it stands right now the improved health and range mean that defenses are superior in a fixed position
It's almost like they're good at defending....sorry, had to do that.
Now onto the ACTUAL reply.
You have to remember that your play style can influence your opinion of balance... if 2 turtles play and build up huge armies before trying to commit to battle then heavy defenses will appear over powered
Actually, I think that's our issue more than anything. We've gotten to the point where all four of us tend to just hole up in our base. I've tried rushing a few times, but after the first 5 or so minutes I just kind of give up with that if I haven't won (high tier stuff is SO tempting). I may try just getting to tech 1-2 and then fighting there for a while to see what it's like and how well it works. You've rather convinced me though. I'll leave T2 defenses as is until more testing has been done on it (specifically with trying to NOT turtle).
Although I must say I love my way of playing superweapons ("Oh, I only have 150 extra power....MORE REACTORS!). Not exactly economical, but I don't run out of power.