So a % reduction to damage taken on Blood Price would be more analogous to Inner Beast or Clemency in terms of where it fits in our kit, rather than PLD's shield. Case in point, Clemency is a DPS loss, both in that it robs you of a Holy Spirit later on and costs a GCD; Inner Beast is a DPS loss in that it requires you to be in tank stance to use, same with Equilibrium. So because Blood Price is now locked behind Grit, it would be a similar DPS loss to rely on for mitigation. Right now none of DRK's mitigation tools are locked behind tank stance, and yet they're mostly lackluster. This would give us the option, if we so chose, to make the sacrifice of DPS for additional mitigation. Granted most of the time we wouldn't want this, but to not even have the choice is a little silly. Souleater's self heal is the only thing locked behind Grit and lets be real, it in no way equates to any of the abilities mentioned for the other tanks.
It doesn't even have to be 10%, I would be okay with it being simply a 10% buff to our defense/magic defense (something like 5-8% less damage taken). Just something to smooth out damage over time.
Dark Passenger's MP cost is ridiculous on all fronts and it needs to be reverted ASAP. Its a bloody travesty of nearly (but not quite) Shake If Off proportions. There is literally no justification for it. They could give it back to us in its original form and with our DPS currently being the lowest of the 3 tanks, it wouldn't throw anything out of balance whatsoever. WAR and PLD have 300 potency attacks on 30s cooldowns with less of a resource cost (if any) than our 100 potency attack that costs 1/4 of our mana on the same recast time. The theme for SB was reducing ability bloat, and if they wanted to make this skill as useless as it currently is, they should have just removed it and baked its potency into something else. Riddle me this SE, how does a 100 potency line AoE cost 2400 more mana than a 525 potency AoE DoT?
DM reducing both damage types I could pass on if they added damage reduction to Blood Price and lowered Shadow Wall's recast and increased its duration. Its great for tankbusters, sure, but our kit is already packed with skills that are great for tankbusters, and none that are good for fluff damage, like Raw Intuition or Bulwark, even as much as those skills have their downsides. However, 15% reduced magic damage for the entire party for 10s while we go right on attacking... I'd draw the line at that I'm afraid. That's almost a tank LB1 for magic damage every 60 seconds. Considering the kind of mitigation you can get with DM+TBN, DADM reducing both damage types isn't just balanced, it makes sense.
Non-DAC&S is fine where it is, especially with the change to Quietus.
I don't think any of these changes are too much. Look at the changes WAR got in 4.05, the changes PLD got in 4.0, AST in 3.4, DRG in 2.45. Almost nothing is too much if people complain loud enough.