Why are you so mad about this? I mean, those greenbeans have nothing. They just vote once a day for a grassblock. Mob arena gives them a chance to earn something better, so they can live at skyblock without having as much as nothing. If you remove this, they might just all quit because they have no better way of getting their items but fighting, which they are mostly I bet not good at. And even if it's a greenbean to some of you donators (I don't disrespect them), I think people quitting is bad.
I don't think DA made this with the intent of having Mob Arena removed, rather, a way to prevent them from obtaining them in a non-legitimate way (such as AFK kicking/void on the sides). Mob Arena rewards are rewards, they are meant to be earned by playing and surviving as long as possible -- but not standing on the sidelines waiting for others to do the work for them, and repeating to achieve the items.
I dont see the issue anymore. The new arenas purpose was to stop people from hiding and encouraging ppl to fight and a new fresh design. Now we see the same problems repeating itself. So obviously it doesnt matter if you afk. Hell, why doesnt everyone get in a big pile and not fight. Because if you want to work for your prizes you work. If you want to be lazy, then be lazy. the only thing i consider not ok is cheating (glitching, riding pets, and /god). Sure it seems unfair, why am i doing all the work? well treat this as what it is... a game. Not everyone will put their all into it, and not everyone plays for the team. But you can be certain that if you love killing mobs, and it makes you happy, you will have fun. forget that you are actually helping those who are lazy, but get those prizes for yourself.
I personally prefer to stay behind warriors/gods and give them (and to myself) a chance by dropping healing and regeneration potions. If someone drops potion of strength for me I'll kick some butts.