People are willing to pay more for the Tubus because of their reputation, because Tubus racks are obviously better made than, say, Topeak racks, and because Tubus racks are attractive (particularly the stainless steel models, which don't rust and don't have a finish that can scratch off). Not necessarily in that order.
That being said, in most cases, a Topeak Supertourist DX will carry as much stuff as you would want to carry. And if you're not going into the boonies, you can limp to a bike shop if anything goes wrong with your rack (and almost certainly nothing will go wrong with your rack).
Heelstrike depends as much on the bags and the chainstay length as on the rack. If you can mount the bags so that any extra bag sticks out from the back, you should be fine with this rack and the Cross Check's chainstays.
I am curious re: how Axiom came up with their rated capacities. It doesn't seem like a remotely good idea to load 154 lbs on a rear rack or 66 lbs on a Journey Lowrider front rack, regardless of how sturdy you think your rack is.