This thread at the MuseScore (an open-source scorewriter) website sheds some light on the Bravura noteheads and is good reading for anyone who enjoys techie/nerdy things. A user there contacted Daniel about design changes to Bravua’s default noteheads in 2015. (MuseScore offers Bravura as one of three options for the musical font.) Reading this makes makes it more clear why the options are named what they are.
If I’m understanding things correctly, the “Larger” noteheads were originally the default glyphs in the Bravura font family—drawn larger because larger noteheads coupled with thicker stave lines arguably aid in legibility. However, since Bravura (the reference font family for SMuFL compliance) is an open-source-licensed font family and can be used in other SMuFL-supported scorewriter applications, it was decided that the default notehead glyphs of Bravura should be a more conservative height of 1 stave space to increase its versatility with programs like Finale that use much thinner stave lines as their default; so the default glyphs for 5 noteheads (double whole note, double whole note square, whole note, half note/minim, black notehead) were reduced in size. However, since the larger noteheads were the original and preferred design choice for use in Dorico, a “stylistic set” of alternate oversized/larger noteheads was added to the Bravura font and included in the SMuFL specifications as “Recommended stylistic alternates”.
So, to sum things up, “Default” uses the default (aka 1-stave space tall) Bravura notehead glyphs and “Larger” uses the oversized noteheads in the “stylistic set” of the Bravura. “Larger” is the original and preferred design choice by the developers.
So, now I totally get why “Default” and “Larger” are called what they are. However, without knowing the background of things, I think most people would assume “Default” equates to the default notehead option for Dorico installations.