Nah, birds are extremely strong for their size/weight, housecats even more so. You're thinking in Earth/human terms. Dwarves are different-not wide, not tall, not big at all, just strong strong strong. And who says they have to weigh as much? Titanium's stronger than lead and weighs a whole lot less.
Dwarves just have a different internal architecture from humans.
And they can probably survive on a diet atleast partly made up of dirt-after all they evolved from earthworms, not monkeys-check your Norse mythology.
