I have similar thinking at first. ARR Beasts are such a pain, comparing to HW Beasts. But they have their own benefits after you have maxed them. Like you mention Anima, doing ARR Beasts will give you faster Unidentifiable items. And there are also exclusive rewards like Mounts & Minions.

Other posts already mention how reputation progression works differently for ARR & HW. I understand you still, though. HW Beasts give good exp and it's just 3 of them per day.

Even though I complained about it, I wanted to complete it anyway. And I have maxed them all finally! Even before the introduction of IV rewards. That's a plus.

But in case they buff ARR reputation like you mention, that wouldn't be nice to those who have spent all those time maxing all, right? I wouldn't mind as much though. But, dang, it would be nice if they buff while I was doing it. It has been a long and not exactly easy for me to complete them all. Good Luck though! Slow and Easy!