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.