How does Difficulty scale damage in Torchlight 2

I made an an engineer with 2:1 VIT to STR, max bulwark and aegis shield, I find that at level 60 he is dying from 1 hit champions, boss attacks a little too often. Also regular mobs are hitting him pretty hard. He is a summoner with many of the +X% to minion damage. This is on Veteran difficulty. I would change to normal, but his minions clearing mobs so fast, they basically die within 1-3 seconds of appearing on the screen. He just walks from room to room basically. My problem is that I do not want to play where I can die from 1 hit, especially with that much defense, yet I cannot set any lower as the game is already easy enough in terms of killing.

I am thinking about making a new char altogether as I do not see this build as viable anymore for me. As for a new character, at which difficulty level would 1 hit kills not be an issue, yet the game still challenging enough? Perhaps better yet, does anyone know what changing the difficulty actually does in terms of scaling (ie: is a simple multiplication factor applied to all monsters damage?)

For the sake of the above example, defense stats: The char also has max healing bot for his level, which is 12).

Solution 1:

You said that you use pets for all your damage and are trying to build up your defensive capability. Have you tried shields? I know one-handed weapons tend not to have as much DPS, but you've said damage is a non-issue atm. Given that you have a high strength score, you would also have a pretty good block chance as well. When you successfully block with a shield, you take 0 damage from the attack (just like dodging.) Getting the right shield should boost your block chance by at least 10%, and give you physical armor passively to boot. This may or may not help you with your 1-hit problem, but if you have a 50% chance to block it should give you at least another half a hit before you go down.