Is it deliberate that it's simply unfinishable? A little notice about it ingame would be nice

I tried turtling them with turrets but they end up destroying more turrets than I can put up anyway. It was only after I read these forums that I got a few hints that this mission is meant to be extremely difficult.
Perhaps it's a good idea to put in a <TIP> Even though we've given you an objective, we haven't finished the next mission yet, so this mission is simply unfinishable.