Marauder's blast has always been more suitable in cracking through defenses before big numbers appear on both sides. Now with Eradicator's long range gun I don't see a role for destructor.
You mean Mauler? I could see choosing Destructors over Eradicators due to faster move speed, cheaper cost, faster build time and AOE but Mauler will do just as well vs. buildings plus of course vs T2s as well. Eradicator is apparently getting AOE on its weapon projectile though, which makes Destructor more obsolete.