No, it's not enough. The game itself tells you it's not enough.
"Too few estates support production and tax collection. Too few estates exert authority and support the local police."
See? Right there. The game is telling you, in red letters, every day, that you don't have enough. Red is bad. Red needs fixed. "Too few" is bad. If the game is telling you that you have "too few" of something then you need more of it. This is doubly true if it's telling you "too few".
The messages the game gives the players drive the reactions of the players. You want them to see 80% as a viable, workable situation? Then when they have 80% you shouldn't be telling them every single day that they need more.
Clarification:
I didn't write the existing estate code, so I can't tell you why it's that way.
