Let me start by stating that I agree with the overall sentiment in the OP and understand the irritation that comes with how things were especially before the correction of the tag being muted by default (good reaction time after discovery btw 
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Ubiquitous Imprecision and Downsides of Over-Precision
The way I see it, the issue is prevalent on pretty much all porn sites. And what leads to misunderstandings, is that everyone makes up the categories as they go and there is no real consensus or logical continuity to what they apply to.
And everyone makes simplifications because, if we were to do it correctly, the granularity necessary (think gender, body parts, group makeup, interactions between actors, the sexual orientation of the actors etc.) is so high, it’s not just admins and mods, but also the creators and users who would have more work to do. And from experience in other fields, even if it is theoretically easier to categorize when the tags are more precise, just by the sheer number of them, more errors will be made which then either creates more work to correct or leads to a lack of trust in the tagging system or both.
Uncertainty Remains with Orientation
So in the end it is the site’s operators that decide these definitions and this will be influenced by wider implicit norms, or like here for simplicity of use for the majority of the user base.
Note that even if we were to introduce orientation tags/tag groups/categories, there will still be uncertainty. For example: When defining an orientation as straight, do the following things belong in there?
- solo-woman (still ok if she’s lesbian?)
- solo-man (and a very straight guy at that so all the straight women have something to look at… or maybe it’s a trans-man at the beginning of transitioning?)
- lesbian (apparently vastly different to gay) twosome, threesome, etc.
- FFM (what if the women kiss… and the other lips as well)
- MMF (what if they high-five while team-tagging her, what if they turn each other on verbally? Is even more okay, because it’s in a threeway? )
- trans-male on trans-female (which gets even more complicated since these categories say nothing about the hardware)
- intersex people
Yes, I’ve chosen these examples to be provocative and sometimes a bit silly, but my point is that there will be a lot of grey area if we don’t go very granular and also there’s individuality in how people define this stuff.
Defining Actions, Actors or User
When we talk about choosing sexual orientations, does that apply to the users, actors or actions? As I tried to show with the previous examples, straight might vary objectively depending on the sex of the user. And even among the same sex and gender, there is an individual component that will never be resolved (classical example among hetero-sexual cis-men when it comes to actions between cis-women).
Pragmatically the only thing that makes sense to me, is tagging the actions portrayed within a piece of media, not to whom it’s targeted (even if it is often done differently). That means that we aren’t tagging gay or straight as an identity, but as a description of occurring actions. We could quickly make this distinction by changing the tag-names to “gay-action” and “straight-action” (and “lesbian-action” for that matter and all others that pertain to it) as well as the respective solo tags. This does not add complexity to the tagging as is, while improving clarity and setting up the future onboarding with orientation tag groups.
There are other axes like gender, sex or hardware (to put it bluntly), etc. that could be resolved in a similar way, but that has to be done with great care to not disproportionately increase complexity.
Orientation as tag groups
If we have described the actions on a reasonably basic level, then the orientation becomes a combination of inclusionary and/or exclusionary tags and tag groups and can then be decoupled from the topic tags for further change and addition in the future. This means that the changes can be initiated quickly and be finished later if the changing behavior is acceptable. Also the distinction of straight man and straight woman is then not on the topic level, but group level, as well as bi-sexual and other groups that are deemed worthy to be assigned during on-boarding.
As an example: If I go to pornhub and choose an orientation out of gay, lesbian and trans, it is just a shortcut to showing the respective category i.e. tags and tag groups. Most probably while excluding tags belonging to the tag group of a different orientation. If I choose Straight, no categories/tags are selected. Note that there also isn’t a category for cis people and the exact sex or gender, neither of the creators nor of the viewer.
The exact definitions can be preset by whatever is decided by the admins and/or user base and can be corrected with the individual tag settings by the user. The difficulty will be to define things in a way that works well with how topics have been tagged in the past.
From where I stand, I believe this to be the least invasive and fastest way to change the structure and process while showing the most respect to everyone.
Since I don’t know the details, I will just point to a possible weakness: How to query the database for topics that aren’t up to par to a new mandatory tagging procedure (if necessary) yet.
As an aside: Only 2 or 3% of the population identify as gay or lesbian
Even if that were to be true (without going into the details of how many problems there are with surveying such a thing), the category Lesbian has been one of the top sought out terms and categories on pornhub for years. The popularity is not tied to the prevalence of a group in society.
