That statement tells me nothing.
The 'they're nice to have but not a necessity' statement could be made about every position but QB.
There are many instances where defenses have been great despite lacking elite players at crucial positions . I'll name just a few...
The '09 NY Jets had a great defense but not one elite DE or rushing LB.
The '08 Steelers had a great defense but not one elite CB.
The '08 Ravens had one of the greatest defenses of all time but not one elite pass rusher with double digit sacks that year. Terrell Suggs led the team with 8 sacks. They also lacked an elite CB. Rolle was the best they had at a past his prime 32.
The '11 Jets had a very good defense but not one elite pass rusher.
These few examples show that a great defense can be formed any number of ways. And all of them show that no position on D is a necessity.
IMO, the logic behind the statement is faulty.