I've known a few Devon's in my life. And the only assumption I'd have before meeting them is that they'd be a female because all the Devon's I've met have been female
Devin seems “correct” to my eye. I have known a Devon but it was pronounced with the emphasis on the O, like DeVON. Devin (to me) puts the emphasis on the first syllable E. To me there may be a ethnic aspect to the pronunciations but not the name itself. I think it’s a good name and don’t think there will be any issues with bias towards Devin/on/en. I also perceive it as a male name. Hope this answers your questions!
Re: Dev-in/on/en