Yep, pretty crappy bomber, yet not the crappiest British bomber of the war.
Had the misfortune of being designed just a few years before the latest WWII developments, and being optimized for one thing: speed. Now, when war rolls around and your only strong suit, speed, is marginal, you get screwed.
Other just-before-the-war designs had better luck, but still fell behind as the war progressed, like the Zero, Bf109, P-40, and B-17. Only a few pre-war designs kept getting better and better, like the Spitfire and Lightning.
End-of-war Lightnings were formidable, with most of their handling quirks ironed out by design, and proved both fast and manouverable. Spitfires kept taking bigger and bigger engines, while maintaing most of their good aspects (and some of their bad), and had a decent post-war career.
The Blenheim was not as bad (or useless) as the Fairy Battle, but it was close. Under-armed, and too slow, they suffered terrible losses.
Still, a torpedo bomber relative of the Blenheim, the Beaufort, dropped a torpedo that won the war in North Africa.
Just before the second battle of El Alamein, Rommel was desperately short on petrol (more so that he usually was) and, in response to his pleading, the Germans and Allies sent a convoy, including a small petrol tanker, the Prosperina. The British got wind in the usual way, and, just before it reached harbor in Tobruk, they launched an attack on it. In the desperate fight that followed, a Beaufort managed to torpedo the tanker which blew up nicely. As a result, Rommel went into the second battle of El Alamein with tanks that couldn’t maneuver.