Youre probably not using it at all if you think building garrison is a golden ability for it.
Don't get me wrong it's pretty situational, but it's definitely one that is useful if you know how to use it. It significantly increases the survivability of the crew and can be instant tank denial of an area if there is a building overlooking a resource point, or if you put it at a choke point on more corridored maps or close quarter sections.
But that's besides the point, shit I made an entire stupid meme video of Tightrope sending a rak across the entire map through enemy lines undetected, and if he wasn't so unlucky he would have gotten a free kill on a katyusha and probably escaped with the rak because it can retreat. You can't do that with any other ATG.