These are precision driving machines. Just get it snug. I doubt that you could compress 11 gauge steel with a normal wrench. But don't try. There's just no need to get it that tight.
I've gone snug on a couple racks and they have never come loose. Tight and then pull hard for a quarter turn or a little less. Most rack hardware seems to come with lock washers. (I don't know the proper name.) They help.
fwiw, I have a couple bolts intentionally loose on my Titan HD, as one of the cross braces is not perfectly square. If I go too tight, the rack goes out of square. Kind of irritating. But the slight looseness hasn't caused any issues.