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I know you hate to see another owl thread but I'm going to put in my two cents. I'm going to compare it to Trevenant, which is an RU mon in gen 6. They have similar stat spreads:
85/110/76/65/82/56
vs.
85/105/80/105/105/65
Decidueye has higher stats overall. What else does Decidueye have over trevenant: Sucker Punch which is a good move, Spirit Shackle, which is an okay move, and higher special attack which is kinda decent. Whereas Trevenant has great defensive abilities that let it function as a good pivot or wall in its tier.
It all depends on the hidden ability, really. But if it gets Natural Cure or Harvest (not likely) it will probably be RU material at least.