Gentlemen, a few things to look at here...
When the Buffalo entered service in December 1939 the Zero was still another 7 months from being deployed. Even as the first aircraft were reaching the fleet, Brewster was already having issues with not only the basic design but also production. I think what we are looking at here is the people who were running Brewster sold the US Navy a bag of goods and were always behind the power curve in not only correcting design problems, but also achieving promised production numbers. The aircraft had potential AFTER it's deficiencies were identified and corrected. From Wiki;
"Pappy" Boyington observed: "But the early models, before they weighed it all down with armor plate, radios, and other [equipment], they were pretty sweet little ships. Not real fast, but the little [aircraft] could turn and roll in a phone booth."
The bad reputation of the Buffalo mainly came out of one battle and that was the mauling VMF-221 received at Midway. By that time the Buffalo was obsolete and so were the tactics being used. Look at those who scored kills and how they scored during the battle - I believe one was from head on, the other was from a diving attack. Also consider the quality of pilots from VMF-221;
"Many of Parks' pilots, fresh from flight training Stateside, had very little operational experience. This fact, combined with the overwhelming size and disposition of the Japanese force posed against the atoll's defenses, would have more bearing on the outcome than the operational capabilities of the F2A."
As indicated earlier, commonwealth pilots had some very limited success with the aircraft and this as a result of experience and tactics. Meanwhile the Finns used their Buffaloes with great effectiveness against the Soviet Union. "Tactics, training, combat experience."
Could this aircraft be considered "One of the worse aircraft ever built?" I think not - I think there were high expectations of this aircraft coupled with criminal marketing by executives at Brewster. This would be further evidenced by strikes, indictments and the eventual take over by the US Government of the company. Eventually the aircraft met it's design requirements, but by that time it was obsolete. With the reputation of this company well tarnished, putting the blame entirely on the Buffalo aircraft was and still is an easy way to smoke screen some of the other issues that plagued this aircraft from its conception - design, production, training tactics. Whether you want to consider the Buffalo one of the worse combat aircraft to every be deployed, so be it, but also consider the operators, tactics and training before painting with one wide brush. If you want to consider it a complete operational failure, there was plenty of blame to be shared on the operator's end as well.