Unless the map is cluttered with players or the map is a turtle map i fail to see where turtle bases are an issue at all. The most common scenario is that 2 opposing players have lots of t1 / some t2 spam when fighting over territory and you try to build some t2 pd to support your army. Note that it's for army support and not to make it act as a "turtle base". These fights are often pretty chaotic so both having the time to build tmd and letting it live is pretty rare. After your mml's have killed the pd's they shoot safely from the back at random units and will eventually give you value as well, since armies tend to grow big enough for them to randomly hit units anyway. You often can build just 2 or 3 mml's and when the fight is over you check the mass killed on the mml's and they often have reached 500+ mass killed, which means they have more than done their job.
This was all talk about teamgames btw. 1v1's turtle bases aren't even worth talking about.