Taking your assertion at face value, that means no full and true democracy has ever existed prior to ~2010. Is that what you believe? Because even the then-believed-to-be freest countries of the 80s were probably quite regressive on gay rights.
You would have to believe that, because otherwise "democracy" seems to mean "all the things that good people support today," which is my point. And if that is what you believe, that only in the last 1-2 decades has a real democracy existed, then you must also believe that it's possible that the science of democracy measuring will discover in the future that the True Democracy is even more democratic than what we have today. It's not clear to me how this is any different from "everything I like is democracy," where "what I like" is increasingly progressive policies.
Why are gay rights apparently part of the canonical definition of democracy and not firearms ownership, which directly empowers people to resist tyranny? How can you explain this by appealing to universal principles, instead of simply reiterating liberal orthodoxy? I don't see a way.
So in a society that sees gays as people, it's not a large leap to consider gay rights as part of a evolving definition of democracy. Same as all western "democracies" took time to let women rights be a thing. Will you argue that a contemporary democracy which doesn't give women a right to vote is a democracy? If not, then how is gay rights different?
In other words, is there a limiting principle that you're appealing to?
And why do you suppose that the right of people directly to be armed, and therefore resist tyranny and remain governed only democratically, never figures into these democracy scores?
I think statistics can be certainly be used to be illustrative. For example, having a 7x higher incarceration rate than Canada might imply that on some level USA has a larger problem than Canada on this democracy level. Specifically, the US disenfranchises people while in prison and frequently keeps them disenfranchised afterward. I'd say it's pretty non-controversial to say that metrics around the percentage of the population living within the country that is enfranchised is a measure of one aspect of democracy (which means that most countries fail on this metric of letting non-citizens vote). Another might be whether citizens believe that an election result was free and fair (in addition to actually trying to find any evidence that it wasn't). A more democratic country would probably engender more good will and faith from its constituents vs one where the population believe that it only paid lip service to the idea.
Anyway, that's all I'll say on this as I'm done talking with someone engaging in bad faith tactics.
Democracy doesn't scale. You need representation. Which makes the question of "what do the people want" very challenging because you go through layers of representation. Definitionally it's a problem which surfaces obviously at the extreme - "if the people want an authoritarian government and they get it, does that mean that that's democracy?". You may think that's absurd yet humanity tends to favor authoritarianism in groups, particularly in moments of crisis and/or being swayed via propaganda (see Julias Ceaser).
I think the nuance that's missing is that you can have objective definitions and measures of democracy which you have dismissed as ""everything I like and want is good and proceeds in a way I'll call democracy" when it's more nuanced.