First message on this forum after reading this nice thread which motivates me to contribute a bit.
I think stg gets "overrated" when its performance/behaviour is (way) below the expectations placed on it, its importance or value is exagerated. Now, from what pov the aircraft should be considered as overrated : public's eyes or air forces/pilots that use it in combat ?
I'll try to answer from these 2 perspectives with only one aircraft. Firstly, the most overrated aircraft should be famous, known by a wide audience, it can't be confidential. IMO that excludes a lot of aircraft of this poll : P-39, some americans bombers (A-20, B-24, B-26, TBF Avenger), Me 210, soviet fighters and bombers (except Yak series and Sturmovik), italian planes, japanese aircrafts (except Zero)... I think that nowadays, these are only known by amateurs/specialists that put a real interest and passion into WWII's aircrafts, or pilots who flew them.
I won't go for the Mustang, the Spit, the Bf 109 or the A6M. The first two may have over-shadowed other aircrafts that contribute a lot in allies' victory but this can partially be explained by the massive psychological impact they had on the British during the BoB for the Spifire and on american bombers crews for the P-51. Beyond these symbolic factors, they were both excellent aircrafts for the role they were initially designated for. I don't vote for the 109 and the A6M for another reason. I actually find quite "unfair" to say that two fighters which dominate the skies for a period could be qualified of overrated. I would more describe them as outclassed in their latest versions rather than overrated.
There's still plenty of aircraft to choose from, so I will introduce another criteria to answer precisely, more related to military specs. When they order a plane, Air forces generally have an idea of the role that it'll accomplish. If the aircraft suits the role there is no problem and no "overrated" aspect. But sometimes, it can be a desillusion. It was typically the case for the Bf 110 which quickly shows its limits against single engine fighter, even at the beginning of the war. However, it had a brilliant "second life" as a nightfighter that illustrates his zerstörer's potential. Same thing can be said IMO for the Hawker Typhoon, mediocre as a fighter but formidable when used as a fighter-bomber.
Nevertheless, it's a bit different for the most overrated aircraft I have in mind, cause I think a better aircraft existed for the same role(s). With that last thing added my vote goes to (drum's roll)... the B-17.
In fact, the B-24 was superior or equal in nearly all aspects : more bomb load, more range, more versatile, same speed, same armor... In the PTO, the B-17 disappears in 1943, because it was unable to do stg the Consolidated can't do. Maybe, the B-17 was a bit easier to handle and build but performance wise I can't see any advantages he enjoyed over the Liberator. In any case that justify the hype he gets, while the B-24 tends to be forgotten.
Thx to all of you who read til the end, hope my non-english speaking doesn't appears too much haha