I think it depends a lot on what the author wants to say with the character.
For example, both Ortega and Dr. Mortum are pretty much the same character regardless of gender in my head. For Mortum there’s almost no difference, while for Ortega there are some between Ricardo and Julia, mainly about their relationship to their family, sexuality and some other small things. Easy enough to write in some variables for. Ortega will be seen differently depending on the gender, and it is interesting to see how the players view them despite 99% of the dialogue and actions being the same. They both end up different people due to gender preconceptions.
When I introduced Argent and Daniel as RO’s I was toying with the idea of making them gender selectable and do a Rebirth bug fix. I choose not to, as there were gendered things there I wanted to explore. Had Daniel been gender selectable from the start, I bet many would have said it was obvious he was written to be a woman. I wanted to explore him without risking that, because I felt that it was important to the character not to be dismissed like that just because he had softer sides as a man. Argent would have been easier, but exploring her pitfalls as a self-created perfect woman had a very different feel than if she had been a man. And Chen, well, yeah. He would have been easy enough to switch, but I didn’t think it was worth the effort at that point.