I don't think it is obvious that measure is meaningful though. The US has always been explicit that it doesn't trust the majority of the population to make decisions and has built intentional systems to keep them out. That is still democratic, the people could change those systems if they really put their mind to it, because the power does technically flow from the people if they really put their foot down.

It is pretty safe to say that the US could be more democratic. It is probably reasonable to compare it to other countries in terms of how democratic it is. But saying it is "not a democracy" is a fairly trivial observation. Republics aren't technically democracies if democracy means that the people make the decisions and win on all the disagreements. Republics are modelled on places like Rome that had a very visible and powerful oligarchy.