It's probably best Star Trek didn't have a gay character though. I doubt any of those writers would have been able to write a gay characters and just have it be a part of his life rather than his entire life, and then every single time they did an episode about that character it'd be entirely about his sexual orientation. Especially on Voyager and Enterprise, any gay character would have had no other personality traits than 'The gay guy'.
I imagine if they'd sat down and said 'Let's write a gay dude' that's probably exactly what we'd have gotten, yeah. But from what I know, Andrew Robinson just showed up and started playing Garak that way unprompted. Imagine if they'd kept (what I assume to have been) their original plan for the character, and just rolled with Robinson's interpretation. That might even have been groundbreaking (I wouldn't really know, I'm no expert on TV history).