Padding is unnecessary, and in fact a nuisance in a working bag, which these are designed to be. And the lack of padding makes it easier to fit odd-shaped pieces of gear in, and allows the bag to conform more readily to your body, thus making it easier to move through crowds. If you're worried about protection, remember that the main compartment is surrounded by pockets which will do just fine in adding layers of protection to that main compartment.
The strap is no worse than any other stock strap out there, but most of us use the super-comfortable Domke Post Office pad, the same one the USPS letter carriers use on their mailbags
Again, they're designed so you can work out of them, not just carry your gear around sealed tightly up. The flap is plenty secure, provides lots of protection, ands yet is easy to get past when you need a lens change.
Canvas does a very nice job of swelling up to prevent water coming through. Unless I'm out in a torrential downpour, the Domke bag needs no extra protection; if it's really that bad, I use a plastic garbage bag.
They may not be cheap, but they last forever, so the cost isn't as bad as it would be on a coated nylon bag you needed to replace in a year or two because it wore through or the lining peeled.
Remember - the Domke bag is a bag designed by a working press photographer, for, and with continual feedback from, working press photographers. And it fills that bill admirably.