Bastion
It takes me a bit to shake off the brain cobwebs, but I eventually get to the point.
Basically if you want to build a tanky character you need to layer your defenses, simply stacking X wont get you there. Having said that if you look at the layers you need vs the investment those three items get you where you need to go. The tanky core of your build is handled by those 3 items, partly because the only other “real” non-item options are in Rogue and Primalist, excluding “active defenses” like rebuke etc. Rogue having dodge/glancing blow, and BOTH having access to flat DR when at Low Life allowing for double DR dipping via endurance. The concern is valid, I do not think there is some magic item or skill/ability that is simply hidden waiting to solve the problem.
It is what it is, do I wish it was different? Yes it should, but we don’t live in Should.