Thanks for this wonderful idea. I have only 2 beast tribes remaining and I can shave 16 days off by using this method.
T1: 15 pts per day -> 150 pts to complete -> 10 days to level.
T2: 21 pts per day -> 360 pts to complete -> 17 days to level.
T3: 30 pts per day -> 510 pts to complete -> 17 days to level.
Thus, two tribes complete in 44 days.

Now, if you take for granted T1 must be done concurrently, as you can only do 3 beast quests per day per tribe.
This split method is still faster, as dedicated completion would still required 50 days to complete.