The new rewards are unsuited for an enrage boss
The identity of an enrage boss is pushing yourself to stay at wave 8 for as long as possible. To support this fantasy there needs to be rewards worth staying at level 8 for, especially because waves ramp the unique rewards, not the regular loot (which is a good thing).
The new bis mage Cape is really cool, the minimum hit bonus is nice and buffs other forms of magic over shadow. However the Cape slot is a prestigious slot. This is how many people feel including me. The fire Cape, skillcapes, infernal Cape, quiver, even things like monkey backpacks and the fish sack. These are all prestigious (at least at one point) because they are untradeable and must be earned. But this clashes with the identity of an enrage mechanic. Even in the latest blog, jagex seemed very against the idea.
Don't just give us the slop of compromise, there are definitely suitable trade able rewards that can fit here. Hate Charge scape as much as you want but something like a zulrah scale would be very fitting here.
Tldr untradeable prestigious rewards don't suit enrage mechanics, the boss really requires tradeable rewards worth staying there for awhile. The magic Cape is cool, perhaps in some other content