Dax was Spock of DS9: a character who's wise and you can always rely on and who will help you with its experience. "Talk to me, Old Man" was the line aye. But of course both of its incarnations we could see weren't perfect - none of the DS9 characters were. They all had flaws, highs and downs and that was really nicely captured by the writers. Hell, that's why Ronald D Moore's Galactica worked and was popular because he incorporated similar character writing style.

Anyway, I could and I still can watch episode with Lenara Kahn without projecting our reality onto it - it's a tragic love story of two individuals separated by standards and customs, who play a dangerous game of breaking taboo set by the Trill society. Jadzia and Lenara suffered and so did Ezri when she arrived on the station - new there in this new environment and new body yet still the same among familiar faces. Again feeling the pressure of her home world and culture which she luckily withstand. Few times in the series writers dealt with how a joined individual is perceived, how that works on relations with people. The gender stuff never played back then any significant part of this species - maybe because show was overall written in a way audience didn't have to be explained or educated. Sure, the kiss scene was a controversial one but people moved on; neither in my country this particular episode and scene got any attention.

On the other hand, Discovery Trill plot was barely watchable to me because it was there just to fill quota set by today's media - there's of course a tragedy and love story but it all feels really superficial and forced. Not mention actors performance was poor but that applies to most of the characters in that show.

To sum this up, yes Trill symbionts are perceived for some reason as trans representation. But that is a totally anthropocentric view, from our real world, slapped onto the fictional universe with action set in the future.