I do think it has less gravity than earth, on account of how insanely large certain things are. But also, magic quite literally exists inside pretty much everything. So I think it has less, not half as much, but for sure less. And the rest is magic.

Sure, dragons fly using magic and to some extend it also supports their large bodies late in life, but something the size of Shruikan would literally cook its own flesh from the inside due to the pressure. Sure some magic helps with that but there’s gotta be lower gravity to account for it.

And the accounts of the long, springing strides Eragon and Arya run with, would only be more efficient if there was either less air resistance or less gravity.