Sure I can answer about the serp helm/faceguard.
The issue with the faceguard is that it is the BiS melee strength helm (and general tribrid/prayer helm) yet even though it's a master quest it's honestly not that hard (master quests are like roving elves anyway not things like SOTE/SOTF) and the creatures are only 60 slayer.
Despite that the creatures are statted like they're slayer creatures in the 80s so it's kind of all over the place.
We could've either nerfed the helm or buffed the creatures and given the tier of quest it felt more applicable to balance it around level 60 slayer instead of higher, I can't remember the exact reason why but that was the teams consensus between the two
The faceguard is still going to be a fantastic item to have. It'll equal the strength of a serp helm, have more prayer bonus and be better in tribrid situations whereas serp will be better for things like ToB where you want to poison, or just generally when you want to have more tankiness or poison resistance.
I hope this makes sense, I can clarify if I've missed something