Andrew the Whilly boat is a brilliant but 'smaller' boat: the LWL, WL beam, sail area and projected designed displacement puts it in the same category as Arctic Tern and Walkabout which have very similar numbers.
Creizic's construction without needing so much centreline structure, floors and boards etc means she is the same weight as an AT but with full sheer level side decks. These will greatly reduce down flooding and stiffen the oarlocks and the boat against twisting. Arguably the construction method is lighter.
The lack of 'ends' compared to say AT will further reduce parasitic weight and windage in row mode and permits building it in a shorter build space. Creizic transom could also allow a normal tiller with an offset mizzen arrangement. Creizic will also have less inverted stability to assist recovery, compared to a longer LOA boat on the same LWL with the same deck arrangement.
An AT owner can point to greater forward flare (dryness), motion comfort from balanced above WL buoyancy, WL extention as it heals (though the apparent displacement wave will also elongate as creizic's transom immerses with heal) and LOD spar storage length, that the greater total LOA permits.