The problem with the HH boardgame version is that it appears to simply be a variant of the Repulsive class, whcih is already smaller than both the Desolater and Despoiler - hardly fitting for Horus's flagship/a Glorina class ship that can carry Legion style forces.
I had dismissed the HH boardgame version as well because of the big Repulsive bottom fin, but after looking at this image I'm no longer sure of the dismissal. The bottom center of weapons bay area has the same diagonal lines as the HHCV VS image. The wepons bay are appears to be 5 weapon bays tall as well. Prow looks a bit different from a Repulsive too. Can anyone who has the game post a good image of the ship?
Also regarding Space Marine battle barges during the Great Crusade: Found another bit of text in Extermination just above the ship list. I guess the bit in bold clarifies that M41 style battle barges did exist during the Heresy.
"Battleships or Battle Barges
Battleships are the principal/capital class of warship in the Armada Imperialis
Range 8-12 km in length, though some were constructed far larger.
Battle Barges are any variant or retrofit of Battleship class hulls modified and optimized for use by the Legiones Astartes specifically for Space Marine planetary assault and ship-to-ship boarding actions.
Purpose-built Battle Barges have also been constructed, particularly in the Great Crusade’s later years.In common parlance, any capital class vessel used by the Legiones Astartes exclusively is often referred to as a Battle Barge regardless of the technical truth of the matter."