Something to remember is that Coil has a much larger loot pool. It has all the Wish weapons and Dreaming City weapons, in addition to being a source of crafting progress. Therefore the Coil needs more drop sources in order to provide an equal chance at getting your target drop.
Between bonus objectives, chest drops, milestones, and random “oops all tormentors” waves there are plenty of opportunities to get Brave weapons and trophies. I’m playing a relatively casual amount and I still feel like I’ll easily get all my desired rolls/shinies by the time TFS drops.
The loot pool for Onslaught is set to double from beginning to end. If the grind is difficult now it's only getting significantly harder as time goes by. We need loot focusing and we need shiny drop guarantees
And yet the pool will still be smaller than the Coil’s. Guaranteed shinies kinda defeat the purpose of rarity, but I’d actually like to see them stick around after TFS drops. No reason to FOMO them so hard.
Coil has 10 weapons that come from activity 6 wish and 4 undying. The secret chests drop Dreaming City weapons and one Wish Engram to use for focusing. The Dreaming City Weapons aren't the draw for the activity their actual source is the blind well.
Even if you counted them as a Coil weapons though that only pulls the total to 14. 2 less weapons wouldn't justify half the drop opportunities no vendor resets and no specific weapon focusing because that's insane