I only recently finished the Freespace 1 campaign after years of playing FS2.
I definitely feel like the Hammer of Light were underdeveloped despite their potential to be as threatening and mysterious as the NTF, or even the Shivans. The way they're introduced is great and raises a lot of ideas that the story doesn't really make good on.
The Hammer and the Anvil establishes how devastating their guerilla tactics can potentially be when they show up masquerading as friendly pilots. Then, in The Darkness and the Light, we're thrown for a loop again when the the Taranis and a bunch of Shivans show up, voiding all the objectives outlined in the briefing and hinting that there's a lot more going on with the HoL than them simply being radical splinter group.
The rest of the campaign doesn't really explore much further though. When they show up in later missions, it more feels like they're present just to give us something to shoot at that isn't Shivan. The NTF have a similar introduction in Freespace 2 as a ragtag but dangerous guerilla force with mysterious motives. However, they're much better integrated into the main story, with the Trinity and ETAK project driving a lot of the plot forward. The monologues and SOC missions developed the NTF as a credible secondary antagonist without taking away a whole a lot of the mystery surrounding them.
If the HoL storyline was given a full arc like the NTF in FS2, it could've gone in some interesting directions by giving us insight into the history of the Vasudans and the Ancients; not to mention, expounding on the Shivan's role as the Great Destroyers.
Out of curiosity, have there been any campaigns from the HoL perspective? We've had NTF campaigns and recently even a Shivan campaign

with Trimurti, but I don't remember hearing about any HoL campaigns. Would be interesting to see someone take a shot at something like that.