Firstly, I think this game's focus is on interconnectedness. Other skills and professions feed into each other heavily so that none exist as an island. Slayer breaks this idea because everything that slaying gives you is either converted to gold or fed right back into the slayer loop. Which I think is bad. You kill a monster and get trophies and XP. XP is only used to equip new weapon types and get better tasks. Tasks only give gold and more XP. Trophies are used for 2 things. Tasks and accessories. But those accessories are only used to be better at combat and kill more monsters. This means the only thing that ever leaves this loop is gold. Making it more of a self sustaining island separate form the rest of the game. This is me identifying what I think is a problem.
Now I have 2 ideas for what could help with this. The first one is just give trophies a use outside of just slayer accessories. Maybe fur can be used to make a new type of leather armor. Or maybe instead of using catalysts to reroll leather gear we use fur to do so. Simply connecting trophies to something other than slayer would pull slayer into the general game flow and make it more interconnected.
My second idea is give monsters drops that aren't just trophies. There was another suggestion that mentioned having Jackyls drop leather and meat. I think this is hard to work in with how things are currently set up but if monsters can be worked into crafting drops I think it would be nice. Not replace birds, but give Jackyls as an alternative source. Maybe make alphas t2 and/or 3 leather, Umburas higher, etc.