Completely false statement. Absolutely, categorically, hysterically wrong. It's also easy to test. Go start an ITF with a character with no defense. Take a full load of purples insps to stay at 50% defense. That's just two medium lucks a pop. Do not eat more unless they are about to expire. Stand in a group. Monitor defense.
Now do the same with an SR scrapper, brute and tank with the same slotting for equivalency. The scrapper and brute around 45% defense to all positions and 95% DDR and the tank should be sitting around 56% and 95% DDR.
The actual cascading defense failure that will befall the character without DDR will rapidly become apparent.
No, in normal content it doesn't matter if your defense is at 45% or 200%. Once you're at the softcap on defense, ALL incoming attacks have a 5% chance to hit which is then adjusted by critter rank, level and power adjusted accuracy. This is true whether you're at 45% in normal content or 58% in incarnate content. The floor is the floor.
Yes, it is still true that if you enter a battle having eaten a huge luck, you will get to delay the defense failures caused by defense debuffs, possibly long enough to survive, but eventually those lucks will run out. And the characters with DDR will keep truckin while those attempting to rely on defense and no DDR will fall by the wayside.