This.
Whenever the 6 to 8 number is bandied about, the implication is that sometimes you have few encounters, sometimes more.
But in reality, the game gives zero mandate to the DM and gives out plenty of "rest enabler" tools to players.
Unless you're fine with the whole "dragon eats princess in three days" time restriction (that virtually never happens in published modules) the grim reality is that a long string of easy encounters is a concept that is completely DOA.
The only way to challenge the player characters in practice is to create a single encounter that all by itself is a challenge.
That is, with NO assumption you're going to be able to make the party keep going while in the "red" of resources.
This, for well-built characters, means something many times the DMG definition of Deadly.
It also means the short-long class balance is an illusion.
In summary, what it means is, the encounter guidelines are a complete joke.