Deep Dwarves?

[arandomperson12]

Why are deep dwarves considered so good? They do not regenerate, they have mediocre aptitudes, including -1 to experience, do not have great innate abilities/resistances, and their damage shaving seems small.

[duvessa]

they have high HP and they start the game with effectively unlimited heal wounds

[Reptisaurus]

There damage shaving gets better, and if you get a very specific combination of God and attributes (Mahkleb + vampiric weapon or vampiric draining, ferinstance) they can regenerate their lost hit points really fast by killing popcorn.

So they rarely need their (as previously mentioned) wand of heal wounds with unlimited charges.

[arandomperson12]

The damage reduction still seems pretty small (3.75 average at level 27).

[Sandman25]

HO in plate armour with AC 30/EV 22 vs Titan (max damage 55)

  Code:

           AvHitDam | MaxDam | Accuracy | AvDam | AvTime | AvSpeed | AvEffDam
Defending:     12.4 |     40 |      68% |   8.5 |   100  |  1.00 |      8.5

The same but now it is XL 7 DD:

  Code:

           AvHitDam | MaxDam | Accuracy | AvDam | AvTime | AvSpeed | AvEffDam
Defending:     11.0 |     39 |      67% |   7.5 |   100  |  1.00 |      7.5

Now for XL 27 DD:

  Code:

           AvHitDam | MaxDam | Accuracy | AvDam | AvTime | AvSpeed | AvEffDam
Defending:      9.9 |     39 |      67% |   6.6 |   100  |  1.00 |      6.6

[triorph]

Also their aptitudes aren't mediocre, they're actually pretty good. Good HP, good armour, good dodging, good axes, and the best earth, invocations and evocations in the game. That's definitely enough to create a solidly powerful character, especially when their other key skills (like fighting and experience) are still average.

[advil]

The damage reduction still seems pretty small (3.75 average at level 27).

In addition to what others have said, damage shaving applies separately to individual sources of damage, which can add up more than it seems, especially in the early game. For example it's a rare source of poison that does anything to a DD. I'm not sure damage shaving is intended to have as much of an impact later, but it doesn't really need to.

Have you played much DD? Once you have a healing technique in hand (and the one they start with is already basically more powerful than '5', if tedious later), they're really, really strong, my most reliable winning species personally.