AI uses TML very well to pick off valuable targets, so you really don't want them to set up. It's going to take proactive scouting to find where they are and some quick bomber or gunship strikes to take them out.
Defensively, the upside is that T2 TMD is relatively cheap and can be spammed, but if you're playing for map control you clearly can't defend everything, so going on the offensive is better.
Alternate option: Play cybran and get T3 loyalist bots ASAP and watch those missiles bounce back to the launchers that sent them. lol