That’s not true. My friend owns the new Ions and the Accera and compared both (10,5 US). Without taking into consideration the half size downsizing that is possible for most, the Accera is still 3-4 mm smaller shell in the same size.I've heard higher end Burton (i.e. Ions) have even better "shrinkage" and are smaller in the same size, but comparable against half-size smaller Adidas.
I’ll ask for the photos from him.
This difference is the same regardless of the smaller or bigger sizes cos both Burton and Adidas have shells that are proportionally bigger with each half a size and scale in a linear manner.
Edit: 10.5 US Accera vs 10.5 US Ion, my bud said it’s 4 mm difference