That tiedown really isn't doing much, especially in the event something fails going 75 down the 405 (which, it won't, your setup seems plenty solid). I'd ditch it the tiedown.
Just to ask, what are you worried about failing? The hardware holding the hilift? Ease your senses by using some old fashioned overkill...get some 3/8" grade 8 hardware.
Keep in mind too, you aren't going to want to keep that gear on the roof all the time... the sun will eat everything. Grade 8 hardware will hold up better to the on and off.
Yeah, I was worry about the hi-lift flying off at highway speed. And noted! I will look into stronger bolts. ty