Lets put this in some kind of common sense perspective.
Put a cheap bike rack on a poorly welded thin bumper and you'll have issues.
Put a cheap bike rack on a solid welded bumper and you'll probably have few issues.
Put a well made bike rack on a solid welded bumper and you'll have zero issues.
FWIW I have a DIY bike rack that I made for my 5er bumper, which happens to be solidly welded to the frame. I've welded up all kinds of projects and have welded on the job since I was 23 years old. So I have 40 years of welding experience. I can personally look at a bumper and tell whether it will hold up or not. Some I see need to be reinforced where they connect to the frame.
My bike rack slips in and out of two bumper mounted receivers. It's solid as a rock.
All it takes is common sense to figure out if a bike rack full of bikes will be there when you get done with your trip. After you have it mounted, just grab hold of it and if you can wiggle it pretty easy, then chances are your bikes won't be there when you get home.
Those that have lost their bikes, didn't know their bumpers were poorly welded and too thin to sustain the constant bouncing of the bikes back there. Had they had the bumper reinforced and had they not gone cheap on the bike rack they'd still have their bikes.