Diversity simply means the company is looking for some balance in the hires. So you will try to pick up a hire from an area where you want to lift the numbers.
However, you don't do this at the peril of the company. Believe it or not, there are a lot of very skilled candidates that are available for diversity hires.
I have not experienced the old meme that diversity stops the most qualified candidates from getting hired. I can only assume that those who have experienced it were not trying to balance their teams from the get go. This may be because they were promoted to management over a team that had no diversity and they were ordered to fill spots with only diversity candidates.
I can see that might cause an issue, but even there you can find very good candidates if you try.
I have not personally run into this, nor has any of my management colleagues and friends.
As you say, if there are two individuals of equal talent and you must hire a diversity hire, then yes that individual would be hired.
That's pretty much how it was done before diversity as well, except you would have preferred someone that was in some way more acceptable to you. That may have been because of their race, sex, ethnicity, culture, values, etc..
Not to mention that your in a unique position to provide a service to the company and to it's clients.
You offer a window into the LGBT community to help create new offerings or simply enhance existing ones.
You are also able to help the company develop a better work environment for other LGBT members.
Just because one of the reasons you were hired is because you are LGBT does not mean that was the only reason.
When I hire for diversity, I make sure I'm getting the best candidate. They need to better than all other candidates I'm interviewing, including non-diversity candidates.
If you are looking for the best candidate, where does diversity come into the picture? How does the diversity thing work?
If you have suitable candidates with similar background, will you prefer the one from LGBT community? That's the only way I see where diversity can help you.