I can't accept slim halflings. For me, they are always tubby.

I'm wondering if the models for the animation were actual people of short stature or if they simply manipulated regular models.

Artwork isn't a great way to make the point about the way things 'should' look, in my opinion. Unless it is a definitive drawing, that's just how someone else has imagined and depicted a member of an imaginary race. How your character looks is largely up to you. You can be influenced by other depictions, but they have also been influenced by other people's ideas so they are not some sort of definitive archetype.

The awkward poses and clipping issues, however, I agree with completely. I also think that the halfling models look rather like real-life people with dwarfism, but at least they don't look like children.