it's as old as all the other WMMA divisons. Unless you mean 'new in the UFC' which is short sighted and not really true anymore either (it's been about 7 years now).
w135 is the 'oldest' women's division (if you think divisions only start when the UFC 'invents' them), is that doing better or worse than w115 or w125 today? If a fighter with Dakota's skillset appeared in UFC w135 tomorrow, would it be harder or easier for her to reach the top that division over 125 or 115?
somewhere between 115-125 is where the biggest 'talent pool' for women lies (it's just numbers) and you can see that already, there are a lot of good younger fighters at 125 now and it's arguably better than 115 already. Ppl predicted this before the UFC had the division (again, it's just numbers) and they were right - after a couple of years to shake out the Eyes and Calvillos, here we are with a bunch of standout talent in their mid 20s. Meanwhile w135 is slowly turning into the new women's 145...