Having no nano in Arid is normal, there are mobs with nasty nanodrain.
And for your information: when I'm tanking sec42, chain mongoing drains my nano very fast (8k nanopool, nanodelta imps, casting only imongo/rage), even with pnh/ior. So there are situations where even current nanocosts are very high for continual use. So I have very pesimistic view of the future after rebalance