I am confused between the two shows, because Dax was very clear that each Dax was it's own person not the same as the Dax before him, yet in TNG episode the host it seems like the riker host is Odon and not somebody else?
There is no "official" explanation as to why the two were so different. It's a plot hole between the two series. Any in-universe explanation is just fanwanking.
They were going to initially make Terry Farrell's make up look like the Odan Trill, but after screen tests they didn't like how it looked on her and they didn't want to cover up so much of her face. Along with that, having one person not be able to use a transporter would have been a logistical nightmare so they dropped that as well.
IMO, It would have been better to scrap the name Trill and just make up a new species.