I find the distinction that MacMillan makes between not to mention and the supposedly synonymous let alone and still/much/even less useful: The phrases let alone and still/much/even less reinforce a negative or unlikely statement that precedes them. The still/much/even less constructs reinforce the negativity of the preceding phrase by subtraction -- Negative statement, still/much/even less ...
Game Rant: Amazon Big Spring Sale Deal Let's You Get $25 Worth of Robux for Less
Amazon Big Spring Sale Deal Let's You Get $25 Worth of Robux for Less