Does specialization with 0 defense really beneficial? To me it is a low risk high return job

If you can spend 360 stored turns with 0 defense sure. But anything after that you risk getting multi grabbed.

tyranny techers with maxed out military strat make some pretty brutal retals but i wouldnt run zero defense. 300-400k turrets i will though with lots of missiles. seems to work well with the gdi rules on express.