This adventurer from Tome of Foes could barely be described as having larger head at all.
While this halfling from SCAG, has an evenly proportioned body, with a head that is positively matched to her form – noticeably smaller than her human or elven companion – as well as a hip and torso ratio that is even and limbs that are only slight in line with her size, and which don't taper away.
Even back as far as Out of the Abyss, we have depictions of halflings that are positively normal in their design and proportions, with no odd tapering, no bobbling, and no unbalanced hip or torso measurements.
There are, in fact, more official images of well-proportioned, sensibly designed halflings, than there are of halfings that exhibit the strange body proportions, bobble-heading and nub-feet of the first artwork; if anything it is an outlier, from the early days of 5e before Wizards had fully settled on their design, and when they did settle, it was not on that.
We can even, as it turns out, go to the very same PHB to find two other halfling depictions that are far, far more balanced in their design and depiction, than the page 26 artwork:
This halfling's head matches his smaller body quite nicely – it's clearly in relation, much smaller than his human-sized allies, just like the rest of him. His legs are clearly visible as well – and they have relatively human-like proportions too, without tapering away.
Here, we get a good depiction of a lower body that is a sturdy match for her upper body, and if you forgive the awkward pose (to make the arm position on her right, she'd need to be pushing her shoulder down hard, which her visible shoulder guard doesn't match, though it would partially account for the very wide-pushing hip on the other side), a smaller-than human head which is only a little bit larger than you'd expect on a human of her size.
So, what is it, ultimately, that's wrong with the current halfling models in BG3? It comes down to four points, which combine to create a visual that feels unnatural and wrong to look at.
- The head: As it stands, the head size needs to come down a little bit. It doesn't need to be a lot, but some. Right now, the halfling head is more or less the same size as the human heads, and that's just not good to see. Along with this, the necks are a little bit too long and pronounced right now, and while it's minor on its own, it is adding to and exacerbating the nearby issues.
- The torso: overall, the torso is just a bit too 'big' for the character size and body; this is another aspect contributing to the accidental sense of dwarfism or neoteny or of being juvenile. It needn't be a large change, but the torso should be maybe 90% of its current overall size, compared to the rest of the body for both male and female halflings.
- The hips: Currently, the halfling models end up with the same waist and hip width as their human counterparts, and this feels extremely out of place. The wide hips, solid torso and tapering legs are all contributing to this same impression of dwarfism or neoteny. At best, it makes halflings feel more like dwarves (the race). This is probably the biggest issue, overall, visually speaking. My strong recommendation would be to just bring the hip width in a notch or two; again, it need not be a lot, but bring it in to better match their overall body frame.
- The legs: the design of the legs, or perhaps it is the build of the upper torso – either way, in the current design, halfling males end up looking and feeling unnaturally top heavy. Halfling females just look like they have a soccer field of distance between the tops of their thighs, which is off-putting. This is a minor issue, and fixing the hips should actually alleviate this issue as well.
At the end of the day, the descriptions and artwork we have give Larian a choice of what style for halflings they want to faovur; the current design is off-putting to look at. It doesn't need to be, and it shouldn't be; halflings aren't joke characters. I do want to say again, yes, it could have been worse... but it could be much better, and Larian have a chance still to make it so. Please look hard at your halfling models, and consider making some tweaks.