In the NBA where only 5 players play at a time and 8-9 players make a playoff rotation, quality always trumps quantity. In football, baseball, and hockey there are exceptions to the rule.
The Celtics definitely got quality over quantity.
Moore and Williams weren't even locks to make the team. Johnson is nice, but likely will never be more than a taller Brandon Bass, which is nice, but not irreplaceable.
I do think we didn't need a SG as much as some thought; however, Lee is a quality player.