The theme of powerful characters taking on powerful enemies seems to fit very nicely for characters slaying huge monsters, in the vein of Monster Hunter or (especially) Dauntless. But the Lumen rules seem to be geared towards mowing through hordes of mobs, instead of taking on a single, very powerful enemy.

Also, one of the tropes of such a game is to 'harvest' parts off a monster that can be turned into armor or weapons. That would also be a departure of the proposed 'random loot generation' in the SRD.

Obviously I will let this stew for a bit, but I was wondering if anyone had any thoughts about this.

So I have a few huge baddies, and my solution for this had been having smaller baddies with them more or less. So a big powerful boss, but he has like 5 lower health shield drones on him that have their own Moves and Abilities. I don't know Monster Hunter super well, but it feels like a thing where you could take a similair approach in having modular bits that players could focus down that might award them a drop, and might make the big bad easier, at the expense of not getting to chip away at his health that turn.

This also seems like a place where you could take the classic console RPG approach (for that matter, I think this is even how the Monster Hunter franchise works) and make each part of the bigger monster a separate piece.  Damage the legs and wings until they cannot fly anymore, then the front limbs, no more claws, but we haven't isolated the head, so watch out for bites and venomous spit attacks!

This also lets you have the monster take multiple actions and compartmentalize its various moves in a similar manner to PC sheets so the GM doesn't have to deal with analysis paralysis, either.

As for the random weapons, maybe the random stuff is incidental, but you take those and the other materials to a workshop and make the bespoke gear. Maybe you need one of those incidentals to use as the basic weapon type frame and use the monster mats and some currency to make the custom gear you want. This would be almost animist, with players investing some of their power in their weapon made from monster totems.

I would suggest taking a look at the way LIGHT does that in Vulcan, trading bounties for tags.