Historically, there were three damage boosting components to a full slayer helm - black mask, hex crest, and focus sight. Each of these gave the 15% strength and accuracy while on slayer task, and came from unique slayer monsters. This made the slayer helmet isolated to the skill and obtained through it. In older runescape, the quest 'Smoking Kills' (2008) introduces and unlocks the ability to create the full helmet.
Old school never added these monsters or items from 2010, until now. Instead, Nightmare zone became the poor replacement for getting a full slayer helm, since Soul Wars (the only place you could imbue) didn't exist yet. Ever since, imbuing your slayer helmet has been attached to a minigame unrelated to slayer. But now that might be able to change, or these iconic items could be something new - let me know which one you would rather have:
A: Hexcrest and focus sight once again become core items along with the black mask, to creating the full slayer helmet. Each of them individually would contribute 15% damage and accuracy of their style (hex crest for magic, black mask for melee, focus sight for ranged). Slightly breaking away from convention, it would make sense for osrs to make the hexcrest drop from aquanites, and the focus sight to drop from strykewyrms (matching their primary attack styles), and lowering their slayer levels to match the black mask.
B: Instead of reclaiming their original function as black mask equivalents, these two headpieces find use in their respective styles with unique utility that doesn't require special attack. These would not be meant to replace current metas, but to supplement gameplay, and reward with satisfying numbers.
Focus sight: Only on the first attack, heavy ammo gains 15% minimum hit and 15% increased max hit. This can retrigger after not attacking for 20 ticks
Hexcrest: Spellbook spells cast at melee distance grant 10% accuracy, and curses gain 50% effectiveness (stacks with tome of water)
Which do you like?