Make the HGS a unique option instead of a downgrade from all other 4d 2h swords. Make it live up to its name and model.
Tentative proposed stat changes: 87 speed, 44 cut, 25 pierce; bump up the price
Those stats are just a rough estimation of what would be ideal. The basic idea is to make it very slow but also hit very hard, the Ganondorf of 2h -with similar weaknesses to more conventional picks. Right now, it is merely kind of slow and doesn't hit harder than great swords of similar dimensions. The only thing it has going for it is its weight, which can be as much a liability as an advantage for long, 4d 2h swords.
Compared to other great swords it would still be pretty clearly worse, but with enough difference in the stats to make it attractive to people wanting to try something new. The only 2h with similarly low speed is the Flamberge and it is 32 length longer (yes, I know it uses polearm animations for 3 of its attack directions and frankly the 2h-righswing <> polearm-stab feint is fantastic), so I don't really think it would be too strong given "the competition" as it were. 90% of 2h are just going to use longsword anyways
Let us play at the margins stat-wise a little more.